could be heat exchanger burst internally. check the filling loop is off completely and disconnect it to be certain. to test if it's the heat exchanger turn off the cold water inlet tap and drain some water out of the system. if it doesn't move then that proves that the heat exchanger is faulty
Ian
August 2009
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
