Worcester bosch 28i expansion vessel losing pressure?

2 Aug 2013
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United Kingdom
Hi my boiler has been losing pressure.
I read on the forums it could be the expansions vessel so i bled my radiators (only the tiniest bit of air) raised the boiler pressure from 0 to 0.5bar then pressurised the expansion vessel to roughly 0.8bar (on the foot pump gauge) . I then took the boiler pressure up to about 1.5 and ran for a couple of hours. Afterwards the pressure on the boiler had dropped down to about .3 and the expansion vessel pressure read 0.

This leads me to believe its a faulty expansion vessel.

Could it be anything else? valve? leak in radiators? I dont want to replace it to find its not the problem

Thanks in advance
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if the expansion vessel is faulty, the press relief valve opens and loses water outside, you need to check that the 15mm copper pipe coming from the boiler through the wall outside isn t dripping. so fill it again and check that

which model boiler is it plse
You can't pressurise the expansion vessel properly without de-pressurising the boiler. Steps are:

1. Drain water from boiler / system (drain off point or radiator bleed valve or boiler drain point - NOT pressure relief valve.

2. Leave drain point open, pressurise expansion vessel with air to manufacturer's specified pressure.

3. Close drain point. Re-pressurise boiler and system to manufacturer's specified level - 1.2 bar is usually about right.

4. Run heating. If boiler pressure on gauge rises by more than about 0.5 bar when system is hot then its quite likely the expansion vessel is the problem.

Presumably you've already checked that no water comes out of the Schrader valve on the expansion vessel.
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The water is leaking through the condensation pipe, a considerable amount, i think this is the problem. Nothing through the pressure release.

Anyone know what the problem is or how to fix?

Some other things have mentioned leaking through the heat exchange?

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