Water Pressure on Boiler Drops in Matter of Hours

JakiT

Hi

A few months ago we had the expansion vessel of our Glow Worm condensing combi-boiler recharged and all was OK until after being away for ten days at Christmas.

We were still covered by the policy. Engineer came out yesterday and recharged the EV though said he's ordered a new one anyway (and apparently he's also ordered a new Compression Valve although as far as I know that's not faulty) and another engineer coming out to do that tomorrow. But engineer yesterday said inside boiler dry as a bone and no ruptures on present EV and the pipes as far as he could see OK (and PVC).

But when we put the central heating on later in the day, exactly same thing happened, water pressure drop to zero after half an hour's heat and keep needing to repressurise to get hot water. OK, so it might get fixed tomorrow.

I've heard though that other things that cause this our leaks. There is a wet patch on the concrete in the boiler room which is outside main house, Engineer didn't think this was anything to do with loss of water pressure but only just seen this wet patch since coming back from Xmas, although last Spring when had same problem with water pressure there was no visible wet patch.
The wet patch is not directly under the boiler but a couple of feet away. It looks as if you would have to drill cement floor in order to get underneath anyway.

Any advice from someone in the know much appreciated - thanks.

nicke20

there is a small copper pipe outside on the wall your boiler is on, put a small plastic bottle on it to see if it catches any water when the heating comes on. if the air has leaked out of the pv then the pv will be full of water and their is no give in the system when the water expands as it heats up (its a sealed system) so the prv lets go and water escapes, as it cools the water preasure drops to zero and the boiler will not refire! Preasurizing the system with water from the main will allow it to start, but probably only once, as their is still no airspace to take up the expanding water. you can always have a secondry pv fittedoutside of the boiler

JakiT

Thanks Nicke. I think the engineers have looked at it )and I did try to look it myself when previously this was mentioned) along with the expansion vessel as a possible cause so I think it has been investigated more than once. It is hard to tell when the weather is wet. It is also so small and close to the wall that you would be hard-pressed to get a bottle on it. Do you think it's best to put bottle or plastic bag on it just after the heating's been on? Would it only show up then if there is water escaping?

Many thanks

nicke20

no the bottle go's outside, the copper pipe is where the water from the operating pressure relief valve ends up, it is just a way of checking you dont have a leak under a floorboard or something and instead losing the water outside.
is there a stain down the wall from it?

JakiT

Hi Nicke
No, there's no stain. There is a big damp patch in the boiler room under the concrete which seems to be getting bigger which is consistent with this. Both gas engineers said they didn't think that was the from a leak and the second one said that it could be from anywhere in the house not necessarily in that area which is very worrying.