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!