pressure dropping

[Mel]

Hi, I wonder if anyone can help. We had a new boiler fitted a couple of months ago (an ariston combi boiler). ON the front of the boiler there is a pressure gauge and we have noticed that the pressure is down lower than the manual says it should be. The manual says between 1 and 1.5 bars and ours is showing about 0.5. This stays the same when hot water is used but rises when the central heating is turned on to about 1.5. However, despite this it's working perfectly ok and gives us hot water and heats the radiators. The plumber who fitted it seemed to do a good job when he did the boiler so we had him fit a new bathroom after and we werent happy with his work. He promised to come back and sort out the bits we werent happy with (we hadnt paid him the full amount) but he has never turned up to do this. As we hadn't paid him everything we were quite happy to leave it like this as we can finish off the other bits ourselves, but because of this its put us in an awkward position with the boiler.\We don't want to have to ring him unless we really have to so if anyone here can give us any pointers we'd be really grateful! Is this lack of pressure anything to worry about and is there anything simple we can do to rectify it? We've bled all the radiators and the actual water pressure through the taps is very high if thats any help. Mel.

[The3rd Earl Of Derby]

open the bypass valve somewhere on the piping below the boiler,its a black knob? turn the valve to the open position for 10mins and then close it again.

[TMC]

Had the pressure been dropping anyway? If not and you have bled the radiators as you say this will reduce the pressure in the system.

The pressure should rise as the heating runs as water expands when heated

You could use the removable flexible pipe that fits between the incoming cold main and the heating circuit on the boiler to pump up the system to 1 bar and then monitor the pressure. (Your manual should explain this) If it drops again you may have a leak

(However as it is a new system there may have been some air left in it which has gradually been purged. This would also reduce the pressure)

Tony

[Bookworm]

Some boilers dont now use a 'filling loop' which is what you mean. They have a built in filling system that usually requires a key that the installer usually leaves. Get the Boiler Manual from the maker and it will tell you how to top up the pressure.

[Ed Sirett]

Please read the Sealed CH FAQ. If you have more than about 10 radiators then it's possible that you should have had an extra expansion vessel fitted.

[John Rumm]

I very strongly advise you *NOT* to do this for ten minutes!

If by "bypass valve" you are refering to the filling loop, then all you will succeed in doing is overpressurising the system to the point where the safety release valve is forced to operate, and you end up dumping gallons of water (along with all your corrosian inhibitor) onto the path outside! Once this happens there is always the danger that the valve does not reseat correctly, and you are stuck with a dripping safety pressure relase valve.

If the pressure is down to 0.5 bar then you will probably only need to add a few litres to bring it back to 1 bar - given you have good water pressure from the mains that will only take a few seconds, not ten minutes.

For a good description of the process, see the sealed system FAQ:

the system was fitted recently it is not uncommon to loose a little pressure from it in the first few weeks as all the disolved air in the water is expelled. If however you find that it continues to regularly loose pressure after that, you may have a very slow leak.

[Mel]