boiler pressure loss

[sparky]

Hi all, if the expansion vessel on a boiler has a problem and the prv disharges to relieve the pressure, how much does it relieve it? Does the guage go to zero or just down a tad?😕

 

[Puddle]

Well in theory it will open around 3.5 bar and close again around 3 bar,which is why it causes a hammering sound opening and closing,however 9 times out of 10 it will not reseat so keeps leaking till all pressure and water leaked out
also it is opening usually when hot due to expansion so closing at hot pressure so when system cools even if valve closes and seals,system pressure will be low when cold

 

[sparky]

Ok got it now cheers m8🙂