02-02-16, 10:03 PM
It's a while since I worked on gas and not registered now so don't do it any more. On most combi's there are 6 or 7 conections, there's the central heating flow (1) and return (2) pipes these are 22mm, mains cold in (3) 15mm, (the filling loop will go from this to the heating pipe), DHW (4) 15mm domestic hot water, this goes to the taps, the pipe from the PRV (5) 15mm to the outside, and the gas pipe 22mm reduced to 15mm (depending on pipe run) if its a condensing boiler there will be a (plastic) pipe going outside to a drain.
You shouldn't have to do anything with the expansion vessle as long as its ok, its there so when the water expands on heating it has somewhere to expand into. If the diaphram is damaged then it won't work and when the water expands the only place it can go is out of the PRV, then when it cools there's not enough pressure for the boiler to work?
You should be able to pressurise the system in a few seconds if the system hasn't been drained by opening the valves on the filling loop there may be two one ate each side if the loop,(as its should be removed to prevent contamination but never is).
You shouldn't have to do anything with the expansion vessle as long as its ok, its there so when the water expands on heating it has somewhere to expand into. If the diaphram is damaged then it won't work and when the water expands the only place it can go is out of the PRV, then when it cools there's not enough pressure for the boiler to work?
You should be able to pressurise the system in a few seconds if the system hasn't been drained by opening the valves on the filling loop there may be two one ate each side if the loop,(as its should be removed to prevent contamination but never is).