Leak hard to find - possible pressure issue?

[Commutergirl]

Hi all

Totally new to this forum and hoping for some guidance.

Two weeks ago we noticed a brown stain on our kitchen ceiling. Above it is the bathroom and airing cupboard where our hot water tank is. We have a closed system. The pressure had dropped on our boiler and so we topped it up (have to do this every 6 months) and two days later the stain appears. We drew a line around it and it did not change until yesterday when suddenly it got a lot bigger and the ceiling was damp. Two engineers later and they cannot find the leak. The first one thought it was something to do with the tundish (overflowing when the water released and running down the pipe - which is directly above the stain). The second engineer could not replicate it. We are now waiting for a leak detection company. We have had issues with the pressure in our system before (two pressure valves replaced on the cylinder for example) and we have been told that the expansion vessel and the cylinder itself are not big enough for the house.

Has anyone come across this type of situation before - where the leak itself is intermittent. I wondered if the expansion vessel was full but it does not feel want to the touch. We’re honestly at a bit of a loss and worried the leak detection company won’t be able to find the problem either. Any suggestions would be very much appreciated.

Thanks! Vicky

 

[John.g]

"we have been told that the expansion vessel and the cylinder itself are not big enough for the house."

Can you post the volumes of each which will be labeled on both.?

 

[Marc Bowers]

Hi Vicky, your boiler pressure and your hot water pressure are unrelated. When you topped up the boiler pressure a couple of days ago, has this dropped again? If not, then it’s unlikely to be your boiler/heating circuit. If your heating circuit expansion vessel is undersized then you would see water discharging from a small copper pipe outside and you would probably be re-pressurising every few days when the heating is on. (This shouldn’t stain your ceiling unless the pipework is damaged)
If the expansion has failed in the hot water cylinder then you would be getting a regular discharge into the tundish every time the boiler heats up the cylinder. If this discharge is warm it is likely the ‘TPRV’ is letting by and will need replacing, if it is cold, it is likely to be the ‘PRV’ and may or may not need replacing depending upon the cause. If there is a discharge to the tundish, this could be the most likely cause as (especially when limescale up) the tundishes do have a tendency to allow water to track down the outside of the pipe. Plus the pipework itself is rarely ever checked for leaks so it may also be compromised. A competent plumber should be able to narrow down the cause without the use of specialist leak companies.