Boiler wont mantain high water pressure!

Humblepie

Hi folks,

Recently had gas turned on after it was turned off for a number of weeks. Since it has been turned on, the boiler is firing up as usual but the pressure gauge is sitting at zero. The ideal is between 1 and 2 given it will increase half a bar on ignition.
Anyway, I can fire up the boiler by upping the pressure by allowing more water into the system by adjusting the tap in the hot press. However, it won't increase to any more that .4 or .5 bar max. The boiler will fire and work Ok after adjusting the pressure in the hot press but when the boiler is turned off, the pressure gauge drops all the way down to zero again. It means I have to go through the refilling process again in the hot press. i'm also concerned as the recommended pressure should be 1.5bar

Anyone got any ideas on how to maintain the pressure at 1 even when boiler not igniting ?? (Its a Potterton boiler)

Thanks for any advice...
H

aujopimur

If you'r loosing pressure you have a leak in your system.
If you have a filling loop your mains pressure is too low.
If you have an auto fillvalve its pressure cutoff may be set too low.

Humblepie

Thanks for reply. There is no leak in the system. How do I know if its an auto fill valve? How do I adjust the pressure cut off if its set too low?

thx

crosstownk

Does the pressure rise when you refill the system? If it does and then drops back to zero, you definitely have a leak. The leak may be under a floor or in a similar place where it is not immediately obvious.

Humblepie

When I refill, it will rise to just below 1 bar. Boiler fires up fine then but pressure doesn't increase. Just tried it there and same story. Water also p*ssing out th epressure relief discharge pipe, while pressure needle droppped to .5 . When I turn heating off, the pressure needle falls back to 0 again. Just noticed also that the rads are working OK but the system isnt heating the water in the taps...

Seems unlikely it is a leak as there was no issue prior to having the gas turned back on by my supplier ??
Any help /checks apppreciated.

GopErthike

You've answered it yourself. Your losing pressure through your safety valve. This can be caused by expansion vessel gone, safety valve passing, or your pressure going too high but not actually registering on the gauge. You need a good RGI installer.

Also if your won't go past .5 it might be tank fed.

Humblepie

Thanks GopErthike, it makes sense now that I read it....
Seems strange though that the expansion vessel could be gone, safety valve passing since the issue only arose since the gas was unlocked by the supplier?
Only trying to suss out how boilers etc work since yesterday so still learning....

GopErthike

Ok, what boiler is it?

Humblepie

Its a Potterton System Boiler...installed 5 years ago, newly built semi D house

GopErthike

It's unlikely the vessel is gone, but possible. Could be just the safety valve passing.

Humblepie

thx, whats meant by the safety valve passing ? you reckon I still need an RGI installer ? Nothing else i can check myself ?

GopErthike

I'm afraid so. Unless there is a problem with the filling valve, which a plumber could fix, the problem is most likely in the boiler. It's illegal for anyone other than an RGI to work on a gas appliance.

The safety valve is the pressure release valve.