Combi Boiler Losing Pressure and Auto Air Vent Leaking?
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Combi Boiler Losing Pressure and Auto Air Vent Leaking?

Post by Vesalius » Mon Feb 20, 2017 4:52 pm


I have a Worcester Bosch 240 Combi Boiler sealed system setup, which last week began behaving oddly. Using hot water on demand kept tripping the overheat thermostat; after a few attempts, seeing as I would be away for a week switched off the power. Central heating is seldom ever used.

Returning home Saturday I noticed the pressure gauge was at 0. After re-ressurising to 1Bar (though I may overdone it…installion manual suggests 1/2 Bar sufficient) the automatic air vent leaking — a fast drip. This wasn't noticed until it had somewhat flooded the cabinet and dripped through to the area where the pump is located; then after trying to stem the flow (cap is missing) water began to pour out at lower pressure until gauge had again dropped to 0.

I haven't re-pressurised but the automatic air vent is still dripping slowly and there doesn't appear to be any leak around the expansion vessel or via its valve. Given some of the corrosion in the interior cabinet I suspect this air vent leak has been an ongoing problem.

Unfortunately boilers are not something overly familiar to me, but I can ill-afford a plumber or gas engineer to rectify the problem if I could do it myself. Ultimately, is a leaky automatic air vent the likely cause of persistent loss of pressure and thermostat cut-out? Is there concievably anything I need to know or could be missing before replacing it?

Thank you!

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Re: Combi Boiler Losing Pressure and Auto Air Vent Leaking?

Post by stoneyboy » Wed Feb 22, 2017 7:18 pm

Hi Vesalius,
Assuming the autovent is outside the boiler casing go ahead and replace it.
If it is inside the boiler casing then you must use a registered Gasafe person.

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