Commissioning a central heating system simply means getting the system working for the first time, and naturally you’ll be keen to feel your heating working. But don’t let that prevent you from taking care over this important final stage.
The first step in commissioning is to fill the system so that you can check for leaks and flush out debris. Start by attaching hosepipes to all the drain cocks (on the heating side —there’s no need to touch the hot water side) and open the cocks — this way, if you have got a disastrous leak somewhere, the consequences shouldn’t be too bad.
Open the tap to the feed and expansion tank (or release the ball valve if this is tied up) and let this start filling. Once the water reaches the outlet pipe, part of the heating system will start to fill — how much depends on the position of the drain cocks. If all is well, close off the drain cocks and let the system fill completely. Check continuously for leaks at all the joints; small leaks in compression or pushfit joints can usually be cured by carefully tightening up the fitting a little; soldered joints will have to be remade after the pipe has drained and dried, so try to bear with any such leaks until after the whole system has been filled and emptied.
Check also that the ballvalve in the feed and expansion tank is working properly: it’s likely that the tank will fill, and the ballvalve shut off, several times during the filling session.
When the ball valve does shut off, check the level of the water in the tank: it should be no more than 100mm, to allow for the expansion in volume when the water in the system heats up.
As the system fills, air will become trapped in the branch pipe runs, preventing the system from filling further. Bleed off this air by opening the vent nipples on the radiators one by one, starting at the lowest. Hold a rag under the nipple and be ready to shut it off as soon as you see water dribbling out.
Open the drain cocks and drain the, system. Mend any leaks, then refill and empty again to flush the pipework thoroughly.
Next fit the pump in place. Making sure everything around you is dry, connect up the pump to the control system wiring. Fill the system yet again, and set the pump running for a few minutes.
Drain and refill; now you should be set to warm up the system.
You should call in a qualified engineer to light the boiler for the first time — some mailorder firms offer this service. The engineer will be able to test and alter the flue draught, and check that combustion is safe. With a gas boiler, you could get all this work done at the same time as the gas supply is connected if you leave this part of the work until the end. As the water in the system warms up, check all joints again carefully for leaks.
The final job is to balance the radiators —alter the flow of water through them so that the correct temperatures are achieved in each room. To do this properly, you need two clipon thermometers (which you may be able to hire from your stockist). Check that the pump is operating on its designed setting, and that the boiler is at full operating temperature —usually 80°C. Starting with the radiator furthest from the boiler, open both the lockshield and handwheel valves and clip on the thermometers, one on each end of the radiator just above the pipework. Then close down the lockshield valve until the outlet thermometer reads 10°C less than the inlet one (if you can’t achieve something close to this, come back to the radiator when you have balanced the others). Do this on each radiator, then check them all.
During the first few weeks of operation, you may need to bleed one or two of the radiators a few more times. But if you have to continue doing this, it suggests a fault —perhaps a leaky joint that is sucking air in, or a more serious design fault. Once you are sure the system is working properly, you should add some corrosion inhibitor to the water. This is usually introduced into the feed and expansion tank, and means draining off some of the water first — the manufacturer’s instructions will tell you exactly what to do.