Boiler Issue

Sounds to be like the pressure vessel has failed. If's basically a diaphragm in a sealed box with water one side and pressurised gas on the other. Which moves to accommodate the increase in pressure in a sealed system as the water heats up and expands. Depending on boiler design, may not be difficult to replace.

Al formulated the question :

The expansion vessel diaphragm has either failed, or needs air pumping in via the scrader(sp?)scrader(sp?) valve.

Yup, what they said...

Find the pressure vessel, and look for the car tyre style valve. Give the pip in the middle a push. If nothing comes out, then it needs re-inflating. If water comes out, then it needs replacing.

To inflate, with the system off, drop the pressure in the system by bleeding off a bit of water. Then pump up to 1 to 1.5 bar. Repressurise the wet side and you should be done.

If its leaking, then you can either replace the failed one, or simply abandon it, and add another expansion vessel elsewhere where it might be easier to get at (some boiler makers like Vaillant make them nice and easy to get at - slipped into the side of the case. Others seem to adopt the lets build it right into the back of the case and stick *everything* else in front of it, so you can't get at it without taking the whole boiler apart!):

e.g. Pressure vessel is the sliver thing on the right with the inflation valve looking straight at you:

(if you need a way to keep a system running for a bit with a failed vessel, then partially drain a rad so that there is an air pocket in the top of it)

We have the 20/25 version of this boiler in a bungalow. Before we bought the property where it is located, I think the expansion vessel leaked and the water also destroyed the control box which is below.

As others have said, it?s caused by insufficient expansion space for the water. That said, unless your boiler was installed by a complete cowboy, it shouldn?t dump water on the floor. The pressure relief valve should be plumbed in to carry the overflow into a drain or outside somewhere.

Tim

I'm amazed that a boiler is not fitted with a suitable bit of plumbing to dump water somewhere appropriate, not on the floor, though! Brian

Many thanks for all your constructive replies, guys.

I did manage to get access to the valve that looks and behaves like a bycicle one. I pushed the needle in the middle and there was a *very* weak puff of air came out. Seems the membrane hasn't become porous after all. The heating engineer who did the last service told me the whole tank needed replacing and offered to do it for me on the cheap. I managed to get some more air into it via a car tyre footpump and the range of movement has certainly decreased. Trouble is, the maker's recommended pressure is only 0.5 bar and I can't find an air pressure gauge that reads such low pressure! I'll take a look on Ebay and see what's what. So ATM it's just guesswork on my part. Still, at least there's more air in it than there was!

Thanks again, gents.

you want about 1 bar in there.

Absolute tops.

I'd go for 10PSI - which is about 0.7 bar. Your gauge can probably measure that.