Pressurised system keeps losing pressure


Postby Theo Cupier » Wed Dec 26, 2007 12:48 am

We have a recently overhauled pressurised heating system, with the big, red pressure balancing ball in the airing cupboard.

We know that the pressure in the system should not be allowed to drop below 1 bar and generally we fill it to about 2 bar.

However, we are finding that the system is losing about 0.25bar every week.

So far as I can tell, none of the TRVs on the radiators (or the return valves) are leaking. There are no tell-tale wet spots on carpets around any radiators. None of the seals seems to be weeping. There are no obvious signs of leaks showing through on the ceiling from where pipes might be leaking from the first floor.

So far, I've not left the system to see how far it drops, I've always topped it back up to 2 bar once it nears the dreaded 1 bar.

What's likely happening to be causing the drop in pressure and, short of having all the floorboards up on the ground floor to look for leaks there, is there anything else I can do to stop it?

Is this constant dropping in pressure normal or healthy? SHOULD I be trying to do anything about it?

The system has 14 rads (13 of which have TRVs) working off a Glowworm 18HXi boiler. I probably have to bleed a rad a little (1 of 2 or 3 usual suspects upstairs), every 3 weeks or so, but the pressure drops irrespective of this.
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Postby Perry525 » Wed Dec 26, 2007 11:54 am

This happens when joints are not made properly and water vapour gas is able to squeeze out, while water itself is too thick to leak out.
It means that every joint will need a visual inspection and dodgy ones a wipe over with washing up liquid to spot the bubbles.
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Postby htg engineer » Wed Dec 26, 2007 12:24 pm

Not sure who has told you the system pressure should not drop below 1.0bar - it wouldn't do any harm.

2.0 bar is a little bit too high - the system pressure should be between 1.0 and 1.5bar. The system may cut out at 0.5bar or 0 bar but again wouldn't do any harm.

If the pressure is dropping 0.25bar per week - then it's likely to be a leak on the boiler, radiators or pipework. Or the pressure relief valve is passing slightly.

If you're not wanting to lift floorboards etc - you could add leak sealer to the system, it should be able to sort the leak out as it must be quite small.
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