your expansion vessel is low on air you can diy fix it with a foot pump connected to the expansion vessel on the back it's the red round tank like a tyre made of metal. there is a tyre valve on the expansion tank near the top & when the boiler is empty you add 1.3 bar of pressure... your boiler should now balance & not expand when heating & open the valve.
daniel07971456726
December 2008
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