boiler sticking on (again)

[JF77]

OK, the heating stuck on again last night. Turned the boiler off and let the pump over run.
Then I turned the hot water on and the 3 way valve moved to the bottom and the boiler fired up left this until it tank stat clicked off.
Then turned the heating on and the valve moved to the bottom and the boiler fire up. turned the thermostat down and the boiler shut down.
this is where it sometimes sticks on. The only way to turn it off is to turn the boiler off.
so now I confused!
All the threads seem to point to the 3 way valve sticking, but I know its not and even if it is how does the 3 way valve control the boiler? surely the controller is the only device that can power the boiler?
Also when the boiler stuck on the thermostat has no click.

Ps I only replaced the actuator (Drayton 3way mid position) not the valve last year.


Thanks,
Julian

Read more: //www.diynot.com/forums/plumbing/boiler-sticking-on.347324/#ixzz2EwUyNWPS

 

[Markerpen]

The boiler is controlled by a micro switch in the actuator. The timer and thermostats just motor the valve.
The valve body may be stiff, and preventing full movement of the actuator, or the actuator is faulty.