hot water working ok but not heating radiators, pump is working ok as new but not firing up for central heating. Relay switch is also ok. What else can I check?

Gary Arbuckle, October 2009

The controller sends mains voltage to operate the relay which switches on the pump. When the central heating is active, check that you are getting 240v ac at the relay coil. If you are but the relay is not activated, then the relay is faulty and should be replaced. If there is no voltage at the coil then the controller is faulty and needs to be replaced

big Gaz, January 2011