I,m not a heating engineer , but a leak would also cause the pressure to drop , Pm Slim Willy , he is the man .
To check if expansion vessel needs re-pressurising top boiler up to just over one bar when the system is cold. Put the heating on and watch the pressure gauge..if the pressure rises over 3bar then the vessel is flat. Pressure relief valves start letting water out of the system at 3 bar, so when the system cools down again water has leaked out of the system so the pressure goes down to zero. The pressure relief pipe should goes to outside so you don't notice any leaks. On your boiler the pressure relief pipe is the one to the left hand side closest to the front of the boiler see if you can find where that goes to and if it has been dripping. Expansion vessels can usually be pumped back up but prv may need replacing.
Quote from: evesdad on 29 January 2016, 08:19:52 pmTo check if expansion vessel needs re-pressurising top boiler up to just over one bar when the system is cold. Put the heating on and watch the pressure gauge..if the pressure rises over 3bar then the vessel is flat. Pressure relief valves start letting water out of the system at 3 bar, so when the system cools down again water has leaked out of the system so the pressure goes down to zero. The pressure relief pipe should goes to outside so you don't notice any leaks. On your boiler the pressure relief pipe is the one to the left hand side closest to the front of the boiler see if you can find where that goes to and if it has been dripping. Expansion vessels can usually be pumped back up but prv may need replacing.also if you can get to the expansion vessel valve undo cap when cold, press valve in to release air and if water comes out its knackered. I learned that when mine went and as above my system was running passed 3bar which alerted me to the problem
Quote from: midden on 29 January 2016, 11:59:11 pmQuote from: evesdad on 29 January 2016, 08:19:52 pmTo check if expansion vessel needs re-pressurising top boiler up to just over one bar when the system is cold. Put the heating on and watch the pressure gauge..if the pressure rises over 3bar then the vessel is flat. Pressure relief valves start letting water out of the system at 3 bar, so when the system cools down again water has leaked out of the system so the pressure goes down to zero. The pressure relief pipe should goes to outside so you don't notice any leaks. On your boiler the pressure relief pipe is the one to the left hand side closest to the front of the boiler see if you can find where that goes to and if it has been dripping. Expansion vessels can usually be pumped back up but prv may need replacing.also if you can get to the expansion vessel valve undo cap when cold, press valve in to release air and if water comes out its knackered. I learned that when mine went and as above my system was running passed 3bar which alerted me to the problemDoesn't always mean its knackered. If you can still pump the water out of the other side and pump the vessel up to about 0.8 bar you should be ok. You need to have an open end on the system somewhere to pump the water out of the vessel to pressurise it properly.
its on the heating side open the old one up to release system pressure whip the old one out and stick the new one in a bit sharp and you won't have to drain the whole system.
I've never had much luck trying to get them to re-seat.
The AARV should be at the top of the heat exchanger, it might have a knurled knob that must be loose so that any air in the heat exchanger can vent, The PRV is the safety valve, so if the presure rises to 3 bar it vents to the outside , the other valves are service valves and can be closed so you don't have to drain the whole system, if you close them make sure they are open before pressurising the system (I dont know how or when you do the expansion vessle?) the filling loop is used to fill the system to 1 to2 bar.
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.I put some air in it. It shouldn't be full of air then?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?that seems to be what's happeningYou 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).I put the boiler on and it pressured after a while, but don't know if it'll stay up in pressure, looks like I'll be looking at a new diaphram then? Oh that's way past my diy skillset