Worcester Bosch RD628 CombiBoiler: DHW but no CH aftr Summer

Postby jonathanrugg » Tue Sep 15, 2009 12:41 am

I have a Worcester Bosch RD628 Combi Boiler. The DHW works fine but the CH doesn't ever come on (not used the CH all summer).

I have an electronic thermostat, when I turn up the temperature it indicates it's trying to fire the boiler (flame symbol) but the boiler doesn't attempt to light, no relay sound, spark etc and no sound from the pump.

I've bled the rads and the pressure is at 1.5 bar as indicated. The water in the system seems clear (no black scum).

I pulled off the front cover and have identified what I believe is the pump and heat sensor but the rest of it is a mystery to me (no manual since the boiler was installed when I bought the house); I was hoping to find something obvious like a diverter valve. I read somewhere that the diverter could be stuck on DHW (default setting) if the CH hasn't been used for ages or it might otherwise be a micro switch problem?

I'd be grateful if someone could point me in the right direction, I'm reluctant to call someone out if I can fix it myself.


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