CH leaks

When I had a similar problem I undid the fill valve on the expansion vessel and water poured out - at least there wasn't much doubt about what the problem was!

So you eventually discovered you weren't a bedwetter after all :-)

If he could do this easily he would have done it. He has said that he has very posh flooring and to rip it up would be very expensive. What part of that do you find so difficult to understand?

I had a cracked heat exchanger. It was a condensing boiler, so the leaked water was simply piped to the drain. So have a look at the condensate disc harge (note: *not* the pressure relief pipe - that's entirely different) wh en the boiler is off.

Another alternative, if the boiler is feeding an indirect hot water cylinde r, is a leak from primary to secondary within the cylinder. This would be difficult to spot unless the leakage rate is high enough to cause the heade r tank to overflow, which would happen only if none of the taps in the hous e are run for an extended period...

Someone fitting a floor without a trapdoor. My neighbour has such a posh floor, but he fitted it himself and did it properly, with access under the house.

Mind you, a decent carpet is much nicer to walk on than wood.

Why would running a tap make any difference?

Header tank?

if the hot water store tank is open vented and the heating system is pressurised and leaking into the hot water cylinder then the water level in the supply tank for the hot water tank will rise until the heating system pressure has equalised with the hot tank. It would only be likely to cause an overflow if the heating system was repressurised multiple times without letting any hot water out of the hot water cylinder.

for the non pressurised hot water cylinder. If it was a pressurised cylinder (with an internal leak) then the heating system pressure would rise.

Ah - I see what your getting at. Apologies.

I was just explaining it, It wasn't my suggestion, it is an unlikely scenario IMO.

A PRV, pressure vessel leak, air release valve or rad or pipe leak, in that order seem much higher possibilities. Particularly if there is underfloor heating then :a pipe leak.

I'd have thought a water leak this serious could be heard or observed by some tell tale things like condensation in odd places etc, dampness and other more annoying things like fungal or mould growth in funny places, even a smell in a room. Brian

I agree entirely. From the sound of it, though, the OP (and British Gas) are well on the way to eliminating the likely scenarios, so I thought I'd chip in with something more unlikely :)

That's exactly right. BG are not idiots, they know the likely causes, and indeed we have been working to eliminate them one by one. The trouble is we are approaching the point that serious damage will have to be done to the flooring to pin point the leak and repair it. There is some insurance coverage for tracing and repair but there will be a lot of disruption to carry out the work.

It's unlikely to be a pool of water. Certainly not if you are on sandy soil. Even on clay, depending on what's mixed in, there's a good chance the water will sink in.

I really strongly suggest that you get your own USB cam. You have the most incentive to solve this issue without damage to the floors. Something like this, for £20.

It's worth taking out a couple of airbricks, if you need to.

Some are. Like one who got the CH pump in the wrong way round.

I got a usb camera with a 10metre cable from ebay, about a tenner iirc, it has been very useful and would probably be helpful in the OP case as it could be taped to a long rod and put though a pretty small hole, even if it just eliminated some areas it would help a lot.

I suppose it would not be possible to bypass the suspect pipes by a separate, but permanent and cosmetically acceptable, route? Say via a different room, or a ceiling?