Firstly, make sure the filling key is removed so that no water can enter the system by that route.
Assuming it is removed and the pressure is still rising, it'll be the domestic heat exchanger failing internally and will need replacing, had this fault on many occasions.
Carefree
December 2010
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
