Heating not coming on at controller while hot water works

[TimBhoy]

If I turn the heating on at the controller, it does not activate. Here is what I have to do:
1. Make sure the Hot Water is On - it must be on for following steps to work.
2. Turn the Heating on (at this point it will not work).
3. Turn the Hot Water Off - now the heating comes on.
I can now turn the Hot Water back on at this point and both the water and the heating continue to work.
During this process, the manual thermostat does not click when I turn it until Step 3 of turning the hot water off. At that point, the thermostat clicks and the 3-way valve moves to the heating setting. When I turn the hot water back on, the 3-way valve moves to the middle setting and both work.

[stoneyboy]

Hi timbhoy
If your system has worked correctly in the past the most probable issue is the motorised valve.
If it has never worked correctly then the wiring may be incorrect.
Regards S

[TimBhoy]

Thanks Stoneyboy, but I tried changing the actuator and it has made no difference. I still have to make sure hot water is on, then switch HW off and only then will the heating come on (and I can switch HW back on and it still works).
Next thing to try?

[stoneyboy]

Hi timbhoy
You have not said whether the system has worked correctly in the recent past??
Regards S

[stoneyboy]

Hi timbhoy
You have not said whether the system has worked correctly in the recent past?? This is a key fact.
Regards S

[TimBhoy]

I checked the thermostat and the switched live (Call) is not coming on until I go through the usual procedure of turning on the hot water and then switching off the hot water.
Then if I switch the hot water back on it continues to be live and heating works until the next time I have to go through all this again.

[stoneyboy]

Hi timbhoy
You have not said whether the system has worked correctly in the recent past?? This is a key fact.
It is not realist to help you if you do not answer this question.
Regards S