Central Heating Problem

[Duncan Lally]

Hi We had a new, ultra efficient Glow-worm combi boiler with integral storage tank fitted by British Gas about 3 years ago. They did the usual powerflush thing.

We had a loft conversion done September 2003 and the plumber added 2 radiators to the system. Prior to this, the boiler was relocated from the kitchen to the cellar by British Gas for free. This was because we had originally asked for the boiler in the cellar but they miscalculated the clearances. They also added a couple of extra pipes to help the flow (I presume) as upstairs radiators were not as hot as they should be.

We have had a problem with loss of pressure for two winter seasons on the run. I have had to bleed the two loft radiators and add water to the system on a regular basis. As far as we can judge there are no leaks on the system. There is no problem with the heating or hot water supply from the system.

We have the BG 3 Star service contract. When we have mentioned this previously to the engineers they have said something like "air is getting into the system and finds it's way to the top of the system - it's nothing to worry about."

However, I have not been convinced and recently called an engineer out. He said it was probably a build-up of hydrogen in the system. We had broken the terms of our contract by having radiators installed by a third party. It is rare, he said, that such third parties put back the chemical inhibitors put in by BG. Also, the system should be flushed after new flux has been used. A flush costs £500; inhibitors £30. We paid £30 and he added inhibitors. Under our contract, he also replaced the "blow-out valve" (I think - the thing which gets rid of water when pressure is too high).

There is still a problem with pressure. He filled the system. It's now, on average, at 0.5 but should be at min 1. The system does work fine, however.

He phoned us back to see how it was going and thinks it's very strange that there's still pressure loss. He advised me to monitor the waste pipe (ie the one where the water comes out when pressure is too high). He'll phone back next week to check (pretty good service!).

Any reactions to any of the above? Is this a common problem? Is it likely that it would arise from the third-party work? Can anyone offer another diagnosis? Is the system being damaged, does anyone think? And what should I be doing?

Thanks very much for any responses!

[Set Square]

Are you saying that there are 4 stories in your house - basement, ground floor, first floor and attic? If so, what is the vertical distance between the boiler and the highest radiator? Whereabouts are you measuring the pressure - because there's probably going to be a static pressure difference of more than half a bar between the lowest and highest point. If you're measuring it in the basement, you may need to raise it a fair bit in order to have sufficient pressure in the attic. Otherwise, any dissolved air

*will* end up in the attic radiators. Nevertheless, this should stop in time - unless there is a leak somewhere.

Presumably you would be aware of any water leaking out of the pipes or radiators. I don't know a lot about combis - but wonder whether an internal leak is possible between the CH and HW systems - which would loose pressure but not produce any other external evidence?

[Duncan Lally]

Are you saying that there are 4 stories in your house - basement, ground

Correct.

If so, what is the vertical distance between

Pretty much the height of the house - 30 feet?

Whereabouts are you measuring the

I'm taking the pressure from the guage on the boiler, in the cellar.

No - no leaks anywhere. An interesting idea - I'll mention it to the engineer. Thanks for responding.