pressure loss

18 Oct 2005
Reaction score
United Kingdom
my combi system loses pressure overnight. The boiler heats the water perfectly. If I fill the system up and bleed the radiators it runs perfectly at about 1.5 bar for a couple of hrs then pressure suddenly drops to 0 bar but the boiler continues to run (rather noisily). If left off overnight the pressure will also drop to 0 bar. Most of the piping is in the cellar and I can\\\'t see or hear a leak anywhere. The boiler is a \\\'ferroli\\\' - spelling! Grateful for any advice.
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does it shoot up in pressure also,,,before then loosing pressure ?
could be ur expansion vessell has lost pressure and ur prv keeps reliefing pressure !
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your pressure relief valve (prv) could be faulty and may need to be renewed, one way of finding out is checking the discharge pipe off the prv which should be pipe to the out side usually on the external face that the boiler is mounted on. the prv is mounted in the boiler casing to the lower left so the discharge pipe should visible outside from around that region 15mm copper pipe normally

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