Hi, Any ideas please. My central heating has been running fine up to about a week and half ago when the cold the cold weather hit. Now the CH pump will not shut down it runs 24x7 whether the heating is on or off. I've tried changing the frost stat ( The boiler is in the garage) the pump overrun stat on the boiler and the overheat stat on the boiler and the thing keeps on running. Any ideas? The pump is a grundfoss and the boiler is a Potterton Netaheat Profile 80e. The CH and HW are working fine and the boiler works fine when the timer kicks in. Help!!!