I have an ELM Leblanc gas combi boiler that has started losing pressure since I turned the heating on, it was fine all Summer for hot water only. The pressure is dropping and I see the water coming from the Pressuure relief outlet pipe. There is no leakage during heating but when the boiler is shutdown overnight or during the day it leaks. It is losing about a cup full per day. Is the problem the PRV that needs to be replaced or is it a problem with the expansion vessel ?
hi is there a pressure gauge fitted? if the expansion is faulty, the pressure will be low when cold and high when hot, over 3 bar and the safety will lift.. BUT, its not always the vessel that's the fault, it often is the pipe from the vessel to the system is blocked. in heating mode, more water is heated = more expansion required. regards peter
Yes there is a pressure gage and it never goes above the three bar limit. I plan to remove and replace the flex hose to the vessel but I am trying to understand why it only leaks when cold. I would expect the leak to be present when the water expands when it is hot but it does not.
Thats probably when the metal componets get warm they too expand at different rates thereby sealing any leaks.
The pressure gauge stops at 3 bar because that's the pressure the safety valve opens - if it goes higher than that, run... A couple of Qs: did you top up the water pressure before all this malarkey happened? If the discharge pipe keeps on leaking even with the pressure gauge reading well below, 3 bar, then it'll almost certainly need replacing - once 'triggered', these sods tend to not re-seal afterwards. Can you outline the process here, please; you wake up in t'morn and the boiler is cold. What does the pressure gauge read? You then top it up to 1 bar and turn her on? What does the gauge read then?
I leave the pressure somewhere between 1 and 2 bar and whether hot or cold the prressure does not vary much, a little higher when hot as expected. I assume the PRV is not seating well and is leaking but for some reason when hot it seems to seal. I do suspect that the hose between the pump and theh expansion vessel may be blocked so plan to change that.
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