HSA3 way valve or room thermostat problem? Help

[carp]

I have an oil fired central heating system aprox 18 years old. it consists of a Myson 50/60 boiler Potterton EP6000 programmer with a PTT2 tank thermostat control fitted alongside, Potterton PRT 2 room thermostat and an HSA3 motorised valve in the tank cupboard upstairs.

Boiler has recently been serviced and works fine. Hot water works fine but and I have had this problem before, the CH will not come on when I set it on the programmer and turn room thermostat up. Going upstairs I move the lever on the HSA3 from auto to manual and the CH fires up fine. In the past I have replaced the HSA3 valve and the system has worked OK but every winter recently we seem to have the above problem.

Having read the postings I now understand that the room thermostat does more than just control the temperature. Could it be that the room thermostat is faulty and not signalling to the HSA3 valve to change position.

Any advice much appreciated

 

[seco services]

Sounds more likely the motor has failed in the actuator.
Check to see if you get 230v on the white wire of the valve when heating on, if so then the motor isn't moving the valve to ch position.
As you say the ch works when you select ch manually.