Hi, I'm just looking for some advice. I have a potterton housewarmer 55 that keeps locking out. It seems that once the hot water is at temperature then the boiler goes to lock out. Could the problem be the overheat stat? I'm presuming it's only happening with the hot water as I haven't had the heating on for months so not sure if there is a problem with that too. Any suggestions would be of help. I have had a gas safe engineer round but he seems unsure and "thinks it's the gas valve".