Combi boiler pressure goes high when lukewarm

[codeshot]

My combi boiler pressure reaches the maximum and the release valve lets out water yet the water is only lukewarm (or at least, all the radiators are).

By the time the water is hot enough to heat effectively lots of water has been released to keep the pressure from going over the maximum and when the heating goes off, the pressure will drop to zero. Setting the water temperature quite low stops the pressure going up so high but doesn't heat the house well.

What causes this and is it something I can fix?

[gucciman]

its almost certainly a problem with the boilers in-built expansion vessel and you need a heating engineer to diagnose and repair for you.

[matt1e]

or its been overfilled
or the filling loop is still connected and the valve is passing

[codeshot]

I found this: http://bbs.scoobynet.com/archive/index.php/t-5 09022.html

and: http://www.honestjohn.co.uk/forum/post/index.h tm?t=30923

Sounds like gucciman could be right, or the expansion vessel could just need repressurising. Since this problem was present at the time I moved in it could have been depressurised with a good reason or over a long time rather than just a fault and perhaps it will be a cheap fix.

[gucciman]

i would re-pressurise your expansion vessel and service your boiler at the same time for �50