Our CH combi system has been loosing pressure but there are no signs of leakage anywhere.

Cold-fill pressure nominally 1.5 bar, drops to 1 bar after about 12 hours of use - and safety cut-out cuts out!

We have checked (and tightened) all accessible joints and couplings, without finding any obvious leakage. However, much of the pipework is buried in concrete floors!

Can we get away with putting something like "Radweld" in the system? (Say by filling a radiator, through a vent-plug?)

The boiler is new (12 months ago) but the pipework is {about} 30 years old!

Chas, March 2007

you can use leak sealer in the system, give it a go it may do the trick. you won't be no worse off.

hi-spec plumbing, March 2007

@hi-spec plumbing

Nothing out of the prv - or any radiator vents.

We have ruled out (almost?) everything apart from the supply pipework. Can't argue that whoever did the pipework made a mistake ..... BUT

what we REALLY need to know is "can we use a sealing compound (like "RadWeld") in a heating system?"

... or is that more likely to do something nasty to valves and similar "gubbins"?

Chas, March 2007

is your prv letting by (overflow pipe to out side wall. or maybe your pipes in concrete have a slow leak. copper pipes should never be layed straight into concrete, the lime in concrete rots copper pipe over time. common problem.

hi-spec plumbing, March 2007