how can i find out what's wrong with my heating?

Cath you need to determine if the central heating water pump is actually spinning - your radiators can't get hot if its not working. Turn the room thermostat up so you can hear a click and the pump should start - often if you put your hand on it you can feel some vibration. The pump is usually connected directly to the thermostat so this does indeed seem to be your problem - at this stage, anyway. The pump itself may have stuck though, and normally a gentle tap with a hammer may start it again.

John
December 2007