Need to top up central heating water 1x month...why?

Eusebius formulated on Wednesday :

Well, it certainly will not get better until found and fixed :-)

...and each time you top it up, it dilutes the inhibitor so sludge and rusting radiators more likely.

There will be a pipe which ends outside, with its end open pointing at the wall, probably at the back of the boiler. Fit a sandwich bag over the end, with an elastic bag over it to keep it in place, leave it in place and report back if it collects any water over several days?

Check all radiators, valves and pipework for rusty marks and staining from leaks. Check ceilings on floor below, for signs of leakage from pipes under floor.

Check

Over the years i've had the odd almost imperceptible weep at a compression joint at the rad valve.

More recently top ups were becoming more frequent until wetness was noted on a ceiling and it transpired that a copper pipe had developed a tiny hole.

It still needs topping up occasionally, is there anyone out there who gets away with never having to bother?

the first thing to check is the pressure vessel. if that is ok you may have a leak

I have the answer I don't use water central heating at all. grin, but that was not what you meant. Brian

The Natural Philosopher has brought this to us :

Sandwich bag on the end of the PRV pipe, as above, will pick that problem up.

Yes, me. Is having a non-pressurised boiler seen as cheating?

Yup.

I think that would be the condensate drain which isn't relevant to the OP's problem.

Not if it?s ?pointing at the wall?.

Tim

A lot of plumbers install safety valve blow off turned back to face the wall, putting plastic bag over t hat will tell you if the valve is letting out water .... would eliminate one possible cause.