HEATING CONTROL SYSTEM AND WIRING
Central Heating Control systems can get complicated — the easiest way to deal with them is to buy a packaged system, and follow the instructions.
Even the simple system of programmer and ram thermostat described here can involve fairly complicated wiring runs, with many joints.
The packaged systems usually come with a central junction box — you simply run the cables from all the components to this and then make the connections on a longer terminal strip, following the instructions.
First, decide on positions for the components. A programmer is usually mounted in the kitchen near the boiler — but it can go wherever in the house would be most convenient for you to set it — by the front door, so you can check its settings before you go out for the day; or even by your bed if you like, so you can adjust the controls at the same time as you set your alarm clock.
There is no really good place for a room thermostat — but the best compromise is probably the living room. Place it about 1.5m high, away from heat sources, draughts and so on, but in an open position where it can best sense the temperature of the room.
To keep the wiring runs short, place the junction box as close as possible to the programmer, thermostat, boiler and pump — but fill and flush system drain and repeat.
More importantly, install it where it will be easy to work on, and where the resulting mass of wires won’t look too obtrusive.
Connect the programmer, and thermostat to the junction box using 1.0mm2 cable — the same as is used for lighting circuits. The final section of wiring to the boiler, pump and any motorized valves should be in heatresistant flex; run these flexes clear of the heat then, via a proper joint box, continue the run to the junction box in 1.0mm2 cable. Note that many of the components need more than two conductors — motorized valves can use up to six wires — so you will probably have to use threecore and earth cable, or even two or more cables to each component (in which case label each carefully so you know which conductor of each goes to which terminal).
Almost certainly, all components will need to be properly earthed.
If you’re not sure of the procedure, leave this part of the job to an electrician or heating engineer.
The junction box is the only component which is connected up directly to the main fuse box. It’s easily best to connect this to the power supply from a fused spur type of connection unit.
The hot water circuit should be controlled at the very least by a mechanical valve fitted in the primary pipework — though this will give no control over the timing of the hot water supply, it will at least ensure that the hot water never gets dangerously hot.
Such a valve will have been fitted when plumbing in the hot water cylinder.