Central heating question - leaks...

[Adam]

Hi All,

Time to access your collected wisdom again, if that's OK...

Our pressurised central heating system appears to have a leak. The boiler is a Vokera Mynute 20se. Every couple to three weeks it seems to lose its pressure and needs to be topped up from the mains hose. There appears to be one radiator (the bathroom one, as it happens) that consistently needs bleeding - when I checked the others they were all OK.

Presumably this means that air is getting in somewhere very near this rad. Presumably it also means that water is escaping by the same route. I can't find any sign of damp anywhere near this rad, however, although I've yet to have a concerted attempt to follow the pipes and make certain.

Am I right? Or could the air be getting in (and presumably the water getting out) somewhere else, maybe in the boiler itself? Does the ingress of air definitely mean water is leaking out somewhere under the floorboards, or could it be evaporating up the boiler outlet? Is there an easy way to track the leak down?

Thanks again for considering my CH problems!

Cheers - Adam...

[Andrew Gabriel]

Yes (barring corrosion, but accompanied by a pressure drop would point to a leak)

Not necessarily. The air which gets in dissolves in the water. It comes out of the water when the solubility is reduced, which is likely to be in the boiler where the water is heated. The pipework layout is probably such that any bubbles coming out in the boiler flow tend to get directed into that particular radiator. You can't infer anything about where the leak is from this unfortunately.

I found my leak when the system had been off for long enough to be cooled down for a while. Water drips were then visible. With the system on, the moisture dried as fast as it leaked, and didn't even feel wet.

When you have got the leak sorted, you should replenish the inhibitor in the system which will have been lost by topping up, and I presume also used up in trying to mop up the oxygen leaking in.

[Ed Sirett]

See below.