How To Install Your Own Central Heating System


Installing your own central heating is not a job to be undertaken lightly. It creates a lot of upheaval throughout the whole house, and it takes quite a lot of time (best spent in large lumps, rather than spread over weekends and the odd evening). But it is not all that difficult — if you have some plumbing experience — provided you plan properly in advance.

This comprehensive and detailed post on installing your own central heating, tells you how to take the hard work out of the planning stages by using professionals, and explains in detail the more tricky parts of the installation. The following parts cover the actual work involved in fitting the various pieces of equipment, connecting them up and then testing the entire installation.

The first thing to do is to get a broad idea of how a central heating system operates, and some of the terminology used. At the same time, you need to know what are the main options open to you, and their pros and cons.

central heating pump

Next, you must find out about the actual hardware involved — the brands, prices, availability and so on. There are so many bits and pieces involved that you need to browse through the possibilities for some time — so the best plan is to start by looking through catalogues, rather than trying to see all the components in a shop or builders’ merchants. There are a few firms that operate a mailorder supply of central heating components, and some of these produce thick, fullyillustrated catalogues of components, often including very useful descriptions of what each one does and its advantages and disadvantages over other choices. These catalogues are well worth sending for.

The final pre-installation stage is to plan and design the system.

Central Heating Design

Design is not all that difficult, but many people feel that it is better to hand this part of the job over to an expert — they feel in this way they can be confident that the finished job will actually work and keep them warm. There are two main ways in which you can get your heating system designed for you. Firstly, there are professional design consultants who specifically deal in domestic central heating.

They will visit your home, measure it, and prepare detailed plans and specifications, based on everything they can find out about you, your house and your lifestyle. Such consultants can be expensive. Alternatively, you can use the services of the mail order firms, some of whom offer a design service for a relatively small fee (often refundable if you then buy your components from them). If you take up this service, you will have to draw plans of your house, and be responsible for telling the firm about the system you want; they are unlikely to visit you. To do this part of the job successfully, you need to know a little bit about why a design is important, and what is involved in creating one.


In the UK, the most usual form of central heating to install, particularly in a house that’s already built, is wet central heating.

Here, there is a central boiler where water is heated; this hot water passes through pipes to radiators in each room. The radiators give off the heat from the water to warm the room, and the cooler water then passes back to the boiler for reheating.

This sort of central heating system is by far the most common type in use. The most usual form is the twopipe system.

Boiler: Can be gas, oil, or solid fuel. May be freestanding or fitted into a fireplace as part of a room heater.

Flue: The easiest solution to the problem of flues is to fit a balanced flue boiler. This is a cheap method of getting a flue and is easy to install. You must be able to mount the boiler on a suitable outside wall — see the drawing. You cannot get balanced flue solid fuel boilers. The alternative is to use a conventional flue boiler, which needs a proper chimney. An existing chimney can be used, but unless this was built after about 1965, it will almost certainly need lining. Lining is easy for a gas boiler — a lightweight flexible stainless steel liner can be used. More complicated linings are needed for other boilers.

Pump: Forces water around the system, and means that you can use small diameter pipes. Get one with valve fittings on either end, not plain unions: it makes it easier to remove the pump for repair or replacement.

Flow pipe: Takes the water from the boiler to the radiators. In most systems, each radiator is connected individually to the end of a ‘branch run’ of flow pipe bringing water from the boiler.

Return pipe: This takes the water back to the boiler, and is connected in branch runs identical to the flow pipes.

Radiator: The usual form of radiator in the UK is the panel radiator: a large panel of steel with channels in it through which the water flows. The basic version is the single panel; other types are the single panel convector or high output radiator, which has extra fins welded on to it; the double panel radiator; and the double panel convector radiator. These variations give increasingly more heat output for a given surface area — or to put it another way, occupy less wall space for a given heat output.

Convector: An alternative to a radiator. The heating element is enclosed in a box and heating is purely by convection. These are very compact. Most have an electric fan to increase the output — but fans can be noisy. Skirting heating: A type of convector heater, which gives a very good heat distribution, but long lengths are needed.

Valves for turning radiators on and off, and for balancing the flow of water to each heater so that it will heat the room correctly.

Feed and expansion cistern: UK systems are normally open to the atmosphere: if there is a fault and the water boils then it can easily expand or boil away without causing an explosion. The feed and expansion cistern (often called an f&e tank) is mounted as high as possible above the rest of the system, and is linked to the boiler through the feed pipe —there must be no valves fitted anywhere between the cistern outlet and the connection with the boiler. The cistern receives its water from a ball valve connected to the rising main.

The f&e tank has several functions: it ensures the system is open to the air and not sealed; it provides a small pressure head to ensure the radiators remain full of water; it provides a source of water to the boiler (to prevent explosions) if there should be a leak; and it provides somewhere for the water to expand into when it is heated. In normal circumstances, fresh water does not flow into the system — it’s important to ensure that this does not happen to avoid corrosion.

To provide an easy passage for any steam to escape, the system also has a vent pipe connected to the boiler. The free end of this rises above the f&e tank so the tank would catch any escaping water.

Domestic hot water (dhw): The boiler usually also heats the hot water using an indirect copper hot water cylinder. This works in much the same way as a radiator — inside the cylinder is a coil of pipe, connected to the boiler by feed and return pipes (called primary pipes). The hot water from the boiler flows through the coil, heating the water in the cylinder; this is drawn off at the top through secondary pipes to the hot taps. The cylinder is refilled through a feed or makeup pipe from the cold water cistern, and as with the boiler, there is a vent pipe for safety.

Usually, the dhw primary circuit is operated by natural gravity flow — the water circulates without the need for a pump. This is simple, but requires large diameter pipes and a careful layout — with the cylinder more or less directly above the boiler.

Alternatively, the dhw circuit can be pumped using the same pump as in the

radiator circuit. It is neater, and means you will be able to re heat the water quickly. Microbore: Most systems use smallbore tubing — rigid pipes down to 15mm diameter. For some of the piping to the radiators, you could use instead microbore tubing. This is smaller in diameter (10mm, 8mm and 6mm) so looks less obtrusive if you fix it to wall surfaces; it uses clips like those for electric cables, too, which are simpler to fit than normal pipe clips. It is also flexible to some extent, so you may find it easier to thread under floorboards and through walls.

You can use it for the final branch run to each radiator (unless the radiator is very large) in much the same layout as an ordinary system, but main runs will still need to be the larger smallbore pipes. Alternatively, you can use a different sort of layout, in which radiator branch pipes all run to a single central point, rather than joining up along the way. At this point, the microbore pipes all join up in a single fitting called a manifold which is connected to the boiler.

Control system: All boilers have a boiler thermostat to prevent overheating. But you need other controls if you want to keep fuel bills as low as possible. Control systems to provide economical running can become very complex — and the danger might be that you spend much more on the controls than you would save in lower fuel bills. Most people, however, would appreciate a timer — sometimes called a programmer — which will switch on the boiler or the pump (depending on the design) only when you want heating.

Besides controlling time, you also need some way of controlling temperatures. The usual way is by a central room thermostat —this is sited usually either in the hall or living room and can be preset to a particular temperature; when the room reaches this temperature, the heating in the whole of the house goes off. Much more flexible, but more costly, is to fit each radiator with a thermostatic radiator valve to control the temperature in each room individually.

Hot water needs controlling for safety reasons — if it is too hot, it may scald (especially when it’s going to be used by old people and children). The simplest control for hot water is a thermostatic valve that fits in the primary pipe work and cuts off the flow (whether pumped or gravity) whenever the temperature of the water in the cylinder rises above a preset limit. With gravity flow systems, this is the only control usually fitted — water is otherwise heated whenever the boiler is not switched off.

If you want independent control of the hot water timing, you will have to fit motorized valves in the primary pipework, and check that the timer you use is capable of controlling all the components independently.

Stage 1: Calculate the heat loss from each room of the house in turn.

As long as the outside of a house (or even an adjacent room) is colder than the room you are considering, then heat will flow out of it — and to stop the room growing cold you have to supply heat to it at the same rate. The rate of heat loss varies, partly depending on how cold it is outside, and how warm you want it to be inside. So the first step in the heat loss calculation is to decide inside and outside design temperatures.

If you want a costeffective heating system, it is important to pick both temperatures carefully. If you choose too high an outside temperature, then your heating system will not be able to warm rooms properly in the coldest weather, and you will have to top up

Design temperatures depend on nominal outside temperature and personal preference for inside temperatures for each room You cannot normally fit hot water controls of any type to a solidfuel fired system. If you do want to do this, you will need to fit a special, and rather complicated system.

Fuel supply: A gas boiler is connected to the mains gas supply — a job best left to a qualified gas engineer after you’ve put in the rest of the system. If you use a designandsupply firm, they may be able to arrange for the work to be done. An oil boiler needs a large oil tank and fuel delivery line. Ask your local authority about the regulations governing the position of an oil tank and the fire safety regulations involved. For a solid fuel boiler, you will have to provide a bunker.


Proper design is not a haphazard process but involves careful and systematic calculation taking account both of your needs and the limitations of any system. This is normally divided into four stages.

Stage 1: Calculate the heat loss from each room of the house in turn.

As long as the outside of a house (or even an adjacent room) is colder than the room you are considering, then heat will flow out of it — and to stop the room growing cold you have to supply heat to it at the same rate. The rate of heat loss varies, partly depending on how cold it is outside, and how warm you want it to be inside. So the first step in the heat loss calculation is to decide inside and outside design temperatures.

If you want a cost effective heating system, it is important to pick both temperatures carefully. If you choose too high an outside temperature, then your heating system will not be able to warm rooms properly in the coldest weather, and you will have to top up with some other, perhaps more expensive, form of heating.

If ydu choose too low a temperature then the system will be bigger than it needs to be. With excess heating capacity for most of the year and it will be more expensive to run. In the UK, a good compromise outside design temperature is —1°C: a system designed for this will cope with most normal winter conditions, and only rarely will you need to top up with other heating. In parts of Scotland, a design temperature of —2°C is more sensible; and in the West Country, 0°C may be sufficient.

Many of the same considerations apply to inside temperatures — if they are too low, you will feel cold: if they are too high then your system is bigger than it needs to be. Inside design temperatures are largely a matter of personal preference. Many designers use these temperatures:

Living rooms, etc: 21°C.

Bedrooms: 18°C.

Halls and passages: 16°C.

Bathroom: 21 °C.

Other designers prefer to use 21°C throughout, on the grounds that, particularly in modern houses, almost all rooms may be used as living rooms at some time or another.

The calculations will also take into account the materials from which the house is built —some are better at retaining heat than others. And insulation will affect this, too — see The benefits of insulating.

Stage 2: Decide on the positioning of the radiators.

As a general rule, the best positions for radiators is on external walls, preferably underneath windows — this gives the best heat distribution in the room, especially around the window area.

However, there may not be enough room under the window for a normal radiator of sufficient heat output. In this case, the designer will normally opt for one of the higher output types.

Where there definitely is not space under the window for any type of radiator, another position on an outside wall can be tried — perhaps alongside the window: or the radiator could be split into two, one half on each side of the window. Only if all these approaches fail should radiators be placed on inside walls.

In a large room, or a long one such as a through lounge, you should use two or more radiators to give a good heat distribution.

Stage 3: Decide on a sensible pipe run and then calculate pipe sizes.

The best pipe runs are as short as possible —taking into account the construction of the house. Where possible, pipes underneath floors should run along the joists rather than across them. Doors, and to a lesser extent, walls and fitted furniture may mean the pipes have to make detours, and branch runs may have to be connected rather differently from the layout that appears to make most sense.

Having sorted out what appears to be a sound and realistic pipe layout. It is then necessary to calculate the sizes of pipes needed. Choose too small a pipe, and it will not be able to carry enough heat to the radiators to provide the required design heating load — no matter how carefully the radiators are sized, the room could be too cold. Too large a pipe would be wasteful of materials, and is more difficult to install.

In most cases, sizing small bore piping is not too difficult: 15mm pipe is usually big enough for all but the largest main runs nearest the boiler. For these runs, and for pipes leading to the hot water cylinder, 22mm or 28mm pipe is used.

Sizing a microbore layout can be more difficult, partly because there are more main pipe sizes to choose from.

Stage 4: Decide on pump sizing.

The pump has to be capable of pushing water quickly enough round the circuit to supply the heat required, and powerful enough to overcome the resistance of the pipes themselves. Pumps are usually variable head: they can be set to provide a number of different flow rates. ‘So this part of the design is not usually critical — a ‘normal’ pump will do for most smallbore circuits in ordinary houses; a highhead pump will probably be needed for any circuit with microbore piping in it.


If you use a design consultant, they will come round and take full details of your house and. Your requirements. But if you take the cheaper option of using a mailorder firm, and you want them to do a good job of designing your central heating system, you must give them all the help and information you can.

You need to draw up a plan of the various floors in your house, together with details of its construction, level of insulation and so on, decide what sort of a system you want, and tell the firm of any particular requirements you have. The firm should supply you with squared paper to draw out your plans, and a questionnaire to fill in, but to make sure you tell them everything they need to know, follow this checklist:

Mark in, on your plan, the position of all doors and windows, builtin cupboards, fixed equipment such as baths and washing machines, and any other obstructions that might hinder radiator or pipe positioning.

Mark the direction of joist runs (almost always at right angles to floorboards). State if the ground floor is solid or hollow. Mark in window sizes and window sill heights. Note all room heights.

Give the construction of all external walls —whether they are solid or cavity masonry (and if so, whether the cavity is filled with any insulating material) or timber framed. If the wall is cavity masonry, tell them if the inner leaf is brick or lightweight block – if you do not know, tell them the approximate age of the house: this may help. TIP: As a rough and ready check, look at the colour of the dust when you drill the wall — this will often give a clue. Red, orange or brown indicates brick; grey usually means blockwork — although you might have hit a mortar joint between bricks.

Tell them whether any windows are double glazed, and how much insulation there is in the loft. All these details are needed to work out what the rate of loss of heat is from the house — the better insulated it is, the less the heat loss and the smaller the heating system need be (and the lower your fuel bills). Adding insulation before installing central heating is often worthwhile — see The benefits of insulating.

Decide on the temperature you want IN each of the rooms.

Decide whether you want a conventional or a balanced flue boiler.

If you intend to use an existing chimney tell the firm about it: when it was built: whether it is lined (if you can tell); how tall it is and if there are any other walls or trees within a couple of metres radius. Ask them for their recommendations. If you need an entirely new chimney, explain where it will have to go and again give details of any likely obstructions. If you want a balanced flue boiler, you can check yourself whether there are any problems in positioning it.

Decide on whether you want the hot water circuit pumped or on gravity flow. This may be a matter of personal preference, or may be dictated by your plumbing arrangement.

Decide on your control system. Unless you are confident you know a lot about controls, it is best to go for a package system that will come with all the instructions for wiring up, and probably include speciallylabelled junction boxes to help you with this task, which can get very complex.


With a reliable design for a suitable central heating system at hand, the installation itself is generally quite straightforward. Begin by fitting the most obvious components — the radiators and the boiler.

The last few details here in this post on installing your own central heating looks at the theory behind how systems work, how they are designed and how to go about getting a design done for you — one that suits your home, your plumbing system and your budget. Once the first stage is out of the way you can move into the ‘real’ work of installation with confidence.

This part of the project tackles how to turn all the theory and plans into practice. The physical work involved here is largely a matter of measuring, levelling and fixing securely and neatly — always with an eye on the next stage of making all the connections. But in some cases, installation of a boiler calls for considerable advance planning, particularly to take account of the installation of a flue where you may need to work on the roof and remove a chimney pot.

The last and final part of the section deals with the rest of the installation — routing the pipework (together with some work involving lifting floorboards and knocking holes in walls), making plumbing and electrical connections and fitting the controls.

What you need

Use your design plans and specifications to order all the components you need. Some of the firms which undertake design also supply all the hardware, but it may be worthwhile to shop around for comparable items at local heating supply shops or from mail order firms.

Make sure that you specify the exact items you need in all cases — if you’re in any doubt, take your plans along with you and ask for advice in the shops.

There’s a wide range of items and fittings you need so make a comprehensive checklist of the numbers of each item, the sizes and any other special considerations (some design firms supply such a checklist). Whatever the exact nature of the component, divide the list into identifiable related areas and check off the items within each of the following areas:

a boiler and flue (possibly with a pump) and a threeway motorized valve to divert heated water from the domestic hot water circuit to the radiator circuit and vice versa);,

a number of radiators in different sizes and types with valves, lockshields, vent plugs, fixing brackets and, if you prefer, drain taps that you can attach to one of the valves on each of the radiators;

feed and expansion tank;

supply and connection pipes and cables;

a control system of thermostats, programmers and valves.

You need a number of accessories for installing the radiators and boiler: an assortment of screws and wallplugs for fixing; valves, taps and vent plugs for each radiator; radiator foil to minimize heat loss through walls and contact adhesive or doublesided tape to secure it; PTFE tape and jointing compound and hemp; boiler flue accessories.

fire cement and material for making good and postinstallation decoration.

When all the materials are delivered, check them off against your list and stack them as neatly as possible in a place where they won’t impede your work. Stack them together in their five main groups as specified above.

When you’re satisfied that all the components you ordered have arrived, check your design plans yet again, then carry the radiators to their intended positions. Prop the radiators in position and lay the fittings for each one alongside so that you can check that they’re all ready for the installation. Make sure that you’ve got fixing screws and brackets, valves, vent plugs and blanking plugs for each one.

As you lay out the components, take the opportunity to estimate any difficulties that may face you — for example, check again the direction of the joists and the nature of the wall (stud partition or solid masonry). Don’t forget to check that you’ve ordered the right size of radiator to fit the space available and to give the correct heat output.

The boiler itself may need to be assembled on site — follow the manufacturer’s instructions for doing so and complete the assembly before you attempt to install the boiler. If it’s a wall mounted type, bear in mind that you may need help to lift it into place, and that arranging the flue outlet can be quite a difficult and messy job.


The first job of installation is to hang the radiators, mainly because it gets them out of the way quickly — but partly because it gives you a boost that the job is well under way.

Radiators usually clip onto metal brackets that you screw to the wall. Working out the height at which to fit these brackets is crucial — if the radiator is too high, it may foul on window sills and so on; if it is too low, there will not be room to fix the radiator valves and pipework, and the brackets may foul on the skirting boards.

You need a minimum height from floor level to the bottom of the radiator of about 100mm — about 175mm if you are running the pipes along a skirting board rather than under the floor. A minimum 50mm clearance below the window sill is needed, too.

Lay the radiator face down on the floor and clip one of the brackets into place. Measure down from the bottom of the radiator, and add on whatever height you want the radiator to be above the floor. Do the same from the top of the bracket, and finally from the top of the radiator.

Check all these measurements against the wall, and make sure that both the radiator and bracket will sit in place happily. If not, alter the height of the radiator, and try again. When you are satisfied with the position, work out the height above floor level that one of the screw holes on the radiator bracket will come — use the centre of the elongated hole if the bracket has one.

If you have a number of radiators of

the same size to fit, make a note of the height of the first screw hole in the bracket, so that you don’t have to remeasure every radiator. Do the same for the horizontal spacings between the two brackets on each radiator of the same size.

Having worked out the vertical positioning of the radiator, the next job is to work out the horizontal positioning. In most cases, you will want the radiator to sit centrally under a window. But there are two things to check out before you commit yourself to the position. One is that the pipework from the radiators may foul on the joists — if you can, shift the radiator slightly sideways to avoid this.

Secondly, on timberframed walls you should try, if at all possible, to mount the brackets on studs. If you can’t, it’s better to screw stout wooden battens horizontally across the studs and fix the brackets onto these, rather than rely on cavity wall fixings.

Screw one bracket into place, using a No.10 screw at least 50mm long. Use sturdy wall plugs on a masonry wall. Fit the other bracket similarly. Check with a spirit level on a batten that the clipping points on both brackets are level. Some people like to ensure that there is a slight rise towards the end of the radiator that the vent plug is fitted to.

Make sure the brackets are hanging truly vertically, then fix them firmly in place through their bottom screw holes. You can now clip the radiator over the brackets.

Radiator dressing involves fitting valves and air vents before connecting up. Wheel valves and lockshields can be fitted on either side, flow or return. Fit air vents to both top corners, or just one with a blank plug on the other — some are supplied ready fitted.

Before you hang the radiators, think about painting or papering behind them — the job will be much easier now than when you have finished the installation. Paint the back of the radiators, too.

The next stage is to dress the radiator —that is, you must add any valves, taps or fittings that are necessary. Standard radiators have four screw threaded holes, or tappings, one at each corner.

These are used for connecting valves and so on — you have to do this yourself because the radiator manufacturer does not know exactly what component you want in which corner.

Your design will show you what goes where, but the pattern is usually as follows:

The bottom two tappings are fitted with valves that connect the radiator to the pipework. One valve is normally called a wheel head or handwheel valve — it has a handle on the top so that you can easily turn the radiator on and off.

The other valve — the lockshield — is usually identical, but has a cover over the top so that the valve setting cannot be altered easily. The setting is fixed during commissioning of the system, and is altered only if you want to isolate the radiator completely so that you can remove it, say for repair or so that you can redecorate the wall behind it. Normally, the hand-wheel valve is fitted to the flow tapping, and the lockshield to the return tapping, but this isn’t essential, and in any case, if you are using matched valves they are usually interchangeable.

So it doesn’t normally matter to which of the bultom tappings you fit these valves. If you are using thermostatic radiator valves, fit them in place of the handwheel valve.

One of the top tappings is fitted with a vent plug, from which you can easily bleed air that will be trapped in the radiator during filling, and that may build up from time to time when the system is in operation. Again, it does not matter which tapping the vent plug is fitted to — use the one that will be easier to get at when the radiator is in position.

The remaining tapping is not used, and is fitted with a blanking plug.

All these are screwed fittings, and are made watertight by wrapping PTFE tape round the thread before screwing them into place — see Screwed joints.

You will need a variety of tools to dress the radiators. Vent and blanking plugs are usually screwed up using a large squareheaded Allentype key. Radiator valves come in two parts: the union to the radiator is fitted either with a spanner or a large hexagonal key, depending on brand; the valve part, which is fitted later, is usually a compressiontype fitting.

Some people find it easier to dress radiators before they are hung on the wall. It also makes it easier to see exactly where the pipes will run.

But as a final check, mount the radiators on the wall loosely. Fit the valves by hand without using PTFE tape to check whether you’re satisfied. When you are sure of the final position, dress each radiator properly using PTFE tape and the necessary tools.

If you can’t align the radiator without fouling against a joist, consider whether you can add a drain tap to either of the valves — that way you won’t have to make an unsightly bend in the pipe. The drain tap might be enough to move the valve and its pipe to one side of the obstruction. Fit it between the valve and the radiator. If you need to remove a radiator for decoration, you can always use the tap to drain off the water within it.


Radiators that are fitted on external walls can lose quite a lot of heat to the outside through the wall. You can trap much of this heat loss, and reflect the heat back into the room, by fitting radiator foil to the walls efore you hang the radiators.

You will get the most benefit where the walls are solid brick and you are using single panel radiators: if the walls are well insulated, and you use double panel radiators, much less heat is lost so the benefit of radiator foil is much smaller.

Special radiator foils are sold, but ordinary aluminium cooking foil is almost as good and much cheaper Fix either, using double,0 sided adhesive tape or a cont(ilhesive Or sticky foam pachi, over the wl wle area of the, w4j that will he covered by tin’ radiator.


Installing the boiler itself is usually a matter of following manufacturer’s instructions. The same goes for flueg, too. But an idea of what’s involved will help you decide whether you feel up to tackling this job yourself.

The firm who carried out your design work should have already taken into account the requirements of the various regulations covering boiler installation, but if you are in any doubt, you should check that your installation will comply with them.

There are two main points. First, walls and floors close to the boiler should be noncombustible — for example, a solid floor with quarry tile covering and a thick masonry wall. The regulations on fire protection are a lot more strict for solid fuel boilers than for gas or oil ones.

Second, all boilers with conventional flues need adequate ventilation in the room they are sited in — starving a boiler of air could kill people. Openable doors and windows are not enough — there must be some permanent ventilation opening in the room. Your design firm should tell you exactly how much you need, and how to provide it: usually by fitting airbricks at both low and high level close to the boiler.

Besides these points, make sure you position the boiler where you can easily get at all the connection points, door hatches and so on, and where the pipework running to and from it will be easy to install.

You could connect a gas boiler to the gas supply yourself, but it is better to hand the work over to a qualified gas engineer — if only for the peace of mind this will bring. Have this done last, just before commissioning and testing the system to see that it works properly.

Flue installation depends on the type:

Balanced flue: This is mainly a matter of chopping a horizontal hole in the wall through which the flue will poke. If the wall is a cavity one, make sure that debris doesn’t fall down the cavity.

Slide the flue into place and seal the hole according to the manufacturer’s instructions.

Existing lined chimney: Assuming the boiler is not being placed in an existing recess, you must cut into the chimney some height above the top of the boiler so that you can fit a piece of vitreous enamel flue pipe into the chimney at an angle of 45° to take the flue pipe sections from the boiler — your firm should have supplied you with drawings showing what components to use.

Make a bed of asbestos rope and fire cement at the bottom of the opening you have cut and bed the flue pipe on this. Continue the asbestos rope round the top and sides of the pipe. This will ensure that the joint between the flue and the brickwork is flexible, to allow for expansion. Then pack any larger holes with a 1:3 mortar mix and allow to dry.

If you want to mount a freestanding boiler in an existing recess, you will have to have a register plate made up — a metal plate that is fitted horizontally into the flue above the level of the recess. The boiler flue pipe pokes vertically into a hole cut in the plate. You also need to have an inspection hatch cut into the plate to allow for chimney sweeping — make this as large as possible. Seal all joints between the plate, inspection hatch, flue, and chimney with fire cement.

Unlined chimney: For a gas boiler, this can be lined with a flexible stainless steel liner. To install this, you need to climb on the roof and work on the chimney: get someone to do this if you are not confident of your abilities. You will probably need a condensate drain at the bottom end of the liner — best done by fixing a Teepiece to the liner, with the bottom connection to the drain, and the side connection to the boiler flue pipe. If you can, fit the Teepiece in the chimney itself, for neatness. To do this, you’ll need to cut quite a large hole in the chimney breast.

Now go on the roof and remove the existing chimney pot and the mortar it is bedded in (called flaunching). The pot will be very heavy, and must be lowered carefully to the ground. Take the liner onto the roof, fitted with its ‘nose cone’ — a conical block in the lower end which makes it easy to thread the liner through the chimney. Drop a weighted rope down the chimney to an assistant and tie your end to the nose cone. Have your assistant carefully pull the liner down the chimney as you feed it in.

The top of the liner is held with a fixing plate that you mortar into place on top of the chimney stack. You then slide a terminal into place. Make sure the seal between the chimney and the liner is absolutely gas tight.

At the boiler end, seal the Teepiece to the liner and the boiler flue pipe with fire cement, plus asbestos rope if the gap is very large. Lead the condensate drain out of the house.

Lining a chimney for types of boiler other than gas is really a job for professionals. Prefabricated flue: The installation of these differs enormously, depending on where you intend to install it and on the type and brand you use. You should get full manufacturer’s instructions when you buy — in fact, it would be a good idea to ask for these before you decide which type to install. Bear in mind that they’re not very attractive and that they’ll need to be routed up an external wall.

All-in-all, balanced flues are the best choice. They involve less installation work yet provide greater flexibility for boiler positioning — they’re certainly best for wall mounted boilers. As long as you carefully choose a position that provides ventilation and safety, the only work involved is that of cutting an access hole through the wall — there’s no need to erect scaffolding because you don’t need to get on to the roof, and there’s no need for a lining or any ugly pipes.


Screwed plumbing joints are made simply by screwing the two components together. Like a nut and bolt, until they are tight.

But this won’t make them watertight, so first a wrapping of PTFE tape is applied to the thread of the ‘bolt’ component. Make sure you wind this in such a direction that it doesn’t become undone as you screw it home — clockwise as you look at the end of the ‘bolt’. You need three or four layers to be sure the joint will be watertight.

PTFE tape is easy to use and works well on small threads. But on the larger threads — such as on an immersion heater — and on boiler tappings, you must use jointing paste and hemp. Coat the thread of the fitting with the jointing paste (use a spatula, not your fingers if the paste is the acidic type) then wrap several fine strands of hemp into the threads in the same direction as for PTFE tape. Work some more paste on top of the hemp, then screw the fitting home.

Screwed joints are still referred to in imperial BSP (British Standard Pipe) sizes.


Connecting the boiler and radiators to the water and electrical supplies is the most important part of installing central heating — but it’s also hard and messy work so be prepared.

Connecting up the system is the final part of installing central heating, covering all the pipework involved. As long as you have some experience of plumbing, you should not find this difficult, though it’s almost certainly the largest and most timeconsuming plumbing job you’ll ever do. It’s also a job that occupies every room in the house, so if you can, work fulltime on this stage of the installation, rather than only at weekends or evenings.

There are two main parts to the pipework: the connections between the boiler, the new expansion tank and the hot water cylinder: and those between the radiators and the boiler cylinder circuit.

All the connections are quite complicated, so study your design plans and the illustrations on the following until you’re confident that you know exactly which component is connected to which. Only when you’re fully satisfied should you begin this stage of the plumbing and pipework installation.

The next stage is to install your control system and the wiring that supplies the power — a job made much easier by modern ‘packaged’ systems. Finally, you can fill the system, then hire a qualified engineer to fire the boiler and check all your work.

BOILER AND HOT WATER CYLINDER PIPEWORK The most complicated section of pipe work is that around the boiler. Here, you have the large pipes from which branches run to the radiators, the hot water primary circuit to the cylinder, and the feed and expansion pipes to and from the new cistern.

Your designer will have offered you one of a variety of layouts, depending on your house and the type of system you are installing, and the plans should show in detail the layout of the pipework in this area. But you can’t rely on this to be perfectly accurate and you may have to make minor modifications as you go along. This will probably involve buying odds and ends of fittings — best done locally.

Start by installing the feed and expansion cistern in the roof space. This cistern should be placed as high as possible — at least 1m above the top of the highest radiator, or in the hot water cylinder if this is higher.

Run the feed pipe down to the point where it will connect with a return pipe to the boiler (or right to the boiler itself if this has a separate feed pipe connection). The vent pipe should be crooked over the top of the cistern, and taken up as high above the tank as there is room for. Again, run this pipe down to the connection with the piping round the boiler (it may be connected in a number of places, depending on your design or space).

You might want to take this opportunity to install a new cold water cistern as well — the procedure is much the same as for a feed and expansion tank, except it’s larger.

Boiler/cylinder connections — also called the primary circuit — will vary according to the shape of your house and the system that has been designed for you.

The circuit must be vented properly, both from the boiler and from the domestic hot water cylinder.

The pump/motorized valve arrangement must be sited in the most convenient position on the circuit — it’s often easiest at the boiler end but could equally well be placed alongside the cylinder.

Now you can install the new hot water cylinder. Run the flow and return pipes from it to the boiler connections. Commonly, the boiler has separate tappings for the hot water cylinder circuit, so you can connect the pipes directly into it. With a fully pumped system, you effectively treat the hot water cylinder as another radiator — regard the flow and return pipes as branch pipes off the main radiator run and blank off any unused tappings. In these pipe runs there are likely to be a number of control valves and perhaps an airvent — your design will show you where these go and explain how to install them.

With a gravity flow primary type of circuit you will need to make sure the pipes have a continuous rise from the boiler to the cylinder — there should be no horizontal or downward sloping sections.

You can now make all the connections at the boiler,, which includes the first section of radiator feed and return pipes; again, your design will show you what goes where. The boiler will have largediameter screwed tappings. Use bushes to reduce these to the size of the pipes entering the boiler. Screw into these either straight or elbow fittings that are screwed on one end, and have compression joints on the other — known as male iron to compression, or MIX comp. All the screwed fittings should be made with hemp and jointing paste.

Leave a Comment