Leak in central heating system, how to trace

[ss]

My sons gas central heating (combi, make unknown) requires topping up almost every day, it is a council house and they have came out twice and say the boiler is fine, son reckons about 1 litre top up of water each day. The next stage apparently is for the council to rip the floors up but they do not reimburse for carpets etc so not an easy option. Now with that sort of leakage and he is on 2nd floor one would expect some evidence of a leak, he has also alerted the neighbour downstair to check for damp ceiling etc but all is ok, he is going to get a `damp meter` to see if he can pinpoint anything. None of the radiators have required bleeding of air and all radiators visible pipes are leak free. The pressure on the guage drops from 1.5 to under .5 in one day.

Any thoughts or suggestions, I seem to recall some time ago on this NG about something in the boiler needing pumped up with air? Dont know if that would be relevent.

[newshound]

I wouldn't waste money on a damp meter. My guess would be the pressure relief valve leaking. You need to find out where it goes, then tie a plastic bag over the end which will soon confirm any leak.

[ss]

Thanks for that I will get him to check it.

[Andrew Gabriel]

If the pressure goes very high when it heats up, expels through the pressure relief valve, and then drops very low when system cools, that would be the pressure vessel which isn't working (and nothing wrong with the pressure relief valve, which is doing exactly what it's designed to do). It might need pumping up with air or replacing, but as it's rented, I would leave this to the council.

[WeeBob]

Last year I had a similar problem. The plumber eventually found it by listening.

i.e. filling up the (pressurised) system, and listening while it emptied itself.

Personally I couldn't hear it. But he cracked the problem (after an hour or so). He did take up some floorboards, but in the end not much cleaning up was involved.

[newshound]

Good point. One test would be to switch boiler off for half a day and repressurise when cold. If pressure still drops it is the valve (or another leak). Othewise it could be the expansion vessel.