Either, the filling loop is not completely closed water mains water is entering the central heating, or the expansion tank needs re-pressurising. I posted a detailed "how to do this" yesterday, have a look for"optima 701 pressure rises"
not sure if the links works but it should be on
http://www.howtomendit.com/answers.php?id=163192
LTGF
August 2008
howtomendit.com for free repair help, information and advice.
