DIY Doctor UK DIY Forums

I was wondering if anyone could advise me whre the problem lays with my heating system. I have been in this house for 10 yrs the heating system has been working pretty good for all those yrs but for some reaon there is now a problem with the CH heating system. I normally have the HW set to come on morning and evening an hour each time it comes on like clcokwork twice a day, I have the CH set to off with the room thermostat set quite low, when it gets colder in the winter I set the CH to on and regulate the temperature by turning up the thermostat until it clicks this starts the bolier and the CH comes on with the radiators warming up correctly. Now for some reason the HW works great but the CH does not. When I switch on the CH via the controller then turn up the room thermostat nothing happens, the bolier no longer fires, but if I advance the HW to start the radiators start to warm up, for some reaspon I cannot control the CH independanyly of the HW any longer. This morning as an experiment I left the CH & HW to on via the controller wiith the thermostat set down to very low, when the HW came on as normal so did the radiators start to warm up. Is my problem to thermostat, controller (SIEMENS RWB9) or a failty three way valve. I am confused. Any help would be most grateful.

Further to my post i have experimented with the system. If I switch on the central heating on the controller then turn up the thermostat until it clciks nothing happens, if I leave it then go to the three way valve next to the boiler manually pull the leaver over it fires uop the boiler and it works fine, controllling the temperature via the room thermosat, does this indicate, a problem with the motor, three way valve or central heating controller?