My Bosch heatslave 20/25 seems to be heating up the radiators when only the hot water timer switch is on. The sytem is set for hot water and heat combined but the timer for the radiators is past the switch off time but still the heat is diverted to radiators and not to hot water. Running a bath gets only a small amount before water goes cold and radiators go hot. Help

Wattie, April 2009

It's more than likely the diverter actuator that's failed - that's the little motor on top of the valve. Sometimes it's the valve failed but that's comparitively rare.

Make sure you get the correct spare, there's at least 4 different valves for this boiler depending on its age. Check to see if the motor has 3 wires or 5.

This job should really be done by an engineer because it does involve 240v connections.

Bunslinger, April 2009