Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the cover from the valve
Remove the synchron motor from the valve

Measurement:

CAUTION: If the motor has jammed it could be very hot, take care when removing.
Ensure the motor turns freely and smoothly by manually turning the output gear. As a guide compare the resistance felt when turning the motor gear with a new motor, the motors should feel similar.