Ask The Trades - Print Page

Ask The Trades
https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Weird Combi-Boiler pressure! https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1291116317 Message started by Rob Cridland on Nov 30^th, 2010, 11:25am

Title: Weird Combi-Boiler pressure!
Post by Rob Cridland on Nov 30^th, 2010, 11:25am

Hi all... my first post. Please be gentle! :)

I have a Sabre combi boiler at home and the pressure at cold is around the 1 bar mark. When the central heating is running this goes up to around 3 bar (too high!) - I suspect the expansion vessel will need repressurising, so I have that on my todo list.

However, when the central heating is on and the pressure is 3 bar, if I run a hot tap or a shower it goes down to 1.5 bar!

Could anyone be so kind as to shed some light on why this might be?

Many thanks!

Rob

Title: Re: Weird Combi-Boiler pressure!
Post by thescruff on Dec 1^st, 2010, 2:51am

One should suspect the expansion vessel as you say, but it's strange the gauge drops when you run the hot water, which suggests the hx is pin holed.

Does the pressure rise if you don't use the boiler, or fluctuate if you open and close the taps a few times.

One other possibility is you have too many rads for the size of the vessel, has any been added prior to the problem.