Room Thermostat will not start combi boiler to heat radiator

[boydycx]

The down stairs thermostat will not start the combi boiler to heat the radiators.
I swapped the thermostat from upstairs that will start the boiler with the downstairs one but still no luck.
If i turn it on upstairs it will only do upstairs but if i change the settings on the motorised control valve it will do upstairs and downstairs but the system pressure becomes very high and unstable.
Do you think it is a wiring fault or a motorised valve fault?

 

[breezer]

I am not a plumber or heating engineer.
unless you have changed or touched anything i should say its a motorised valve fault, they do seem to go wrong and get "stuck" often

 

[boydycx]

Thanks for that breezer i will try that. Thanks