How do I drain a pressurised central heating system?
Question:I need to drain, then refill, a closed pressurised central heating system, in order to replace a radiator.
Answers:
if you are replacing a radiator with one the same size there is no need to drain the system just shut off the 2 valves at each end of the radiator and remove by loosening the connection nearest the radiator, remember to put something to catch the water that will come out of the radiator when you start to loosen the connections, assist the draining by opening the bleed valve at the top .
at the lowest point of your boiler system there is a relief valve, turn off either electric or gas which supply's unit and open the valve, turn on hot water taps throughout the home to bleed the lines dry...then replace your radiator and then leave taps open to bleed air back out, including the new radiator.you should be fine
At the lowest point of your heating system there should be a drain off valve, connect a hose to this and the other end to outside the house. Turn off the boiler. Turn on the drain off, when the water has almost stopped running start with the highest radiator and open the bleed screw working down to the lowest. when you have changed the radiator, close all the bleed screws and drain off, refill the system then bleed your radiators starting at the lowest. when this is done, make sure the pressure is set to 1.5 bar. you do not need to touch your taps they are on a different circuit. good luck.
I suspect that you are about to try something out of your reach. If you succeed in draining the system, there is the problem of air addmittance which will cause corrosion.Get an expert for peace of mind. Some systems can ONLY be serviced by a professional, not a handyman or "run-of-the-mill" central heating engineer for insurance purposes
If you need to ask, don't do it. Get a professional.
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