Baxi Genesis Comi Boiler - Hot water is fine & works. Central heating fires up but water does not circulate so rads don't get warm. Also it appears that the pump works therefore I think a thermo valve has gone. Can someone confirm a part replacement where can I get one from and also what is involved in fitting one?

James Seaton, October 2006

The 3 way valve sits in the ch position at rest and moves to DHW position when a tap is opened. The valve may be stuck in the DHW position but you should check the Thermisters (temp sensing device) first. If the ch sensor is reading wrong then the boiler will pump but burner may not come on. They work on resistance ie at 20 degrees c they may read 12000 ohms. As the temp increases the resistance decreases. So if you get a reading of 1000 ohms then the boiler thinks the temperature is over 100. Compare the DHW and CH sensors when the boiler is cold.

kenneth, October 2006