Boiler vessel in trouble

It's probably lost some of its air - and thus reduced its expansion capacity - causing the pressure to rise too much, and water to be expelled through the pressure relief valve.

With the water system unpressurised, you should have something like 0.7 bar (10 psi) on the air side of the pressure vessel. There should be a Schrader valve (like a car tyre valve) where you can measure the pressure and pump more air in. If this is low, top it up to 0.7 bar and then pressurise the water system to 1 bar when cold. Hopefully it won't then rise above 2 bar when hot.

Note: If water comes out of the Schrader valve, the vessel has a split diaphragm, and is shot.

Hi, If there is no sign anywhere of a leak, remove the boiler cover, you will see the pump on the left, about 2in to the left of the pump is a flat red metal expansion vessel. Fitted to it is a "Tyre Inflater valve" Press this in with a match, if water comes out it has failed. You dont have to renew it, as that is a nightmare job, instead obtain an expansion vessel (1 to 3 L) from plumbCentre and fit it in the return line near the boiler. If nothing comes out, use a car foot pump to inflate it to 2 Bar (25psi) If that works but only for a few days, replace the "Tyre inflater valve" (50p from Halfords) Regards Bob

That would likely be far too small. See FAQ.

OK! so use one a Litre bit bigger then ;)

frequently

Inflater

Bob

Many thanks for a very helpful reply. I presume that the new vessel comes fully pressurised. Do I have to do some adjustments after replacing the vessel@

Kind regards Eithera

Unlikely. My comiserations on your having a Saunier Duval bye the way

-- Paul Barker