what is likely problem with Sime 80E Combi boiler only giving hot water if room thermostat is calling for heat. Hot water does not fire if central heating off. Boiler 4 years old and serviced / powerflush last year.

Terry, January 2006

H'i Terry,
The problem with your boiler is the domestic hot water diaphram. This is fitted as part of the diverter valve, but you can purchase seperatly.
After a period of time they become perforated, and concequently dosen't lift the push rod, which operates a microswitch, which in turn operates the boiler in D.H.W mode only.
When your boiler is in HEATING & D.H.W mode, with your room stat calling for heat, you will probable get a limited amount of hot water, also it won't be as hot as normal because the burner flame will be at a lower pressure than when the system is in D.H.W mode, and working properly.
You should pay around £15-£20 for a diaphram kit. Good luck!
Dave.

Dave Williams., February 2006