Sparks wrote:

Unless the actuator is faulty, has stuck on, one side of the
microsowitch is connected to the boiler, and the other is connected to
a permanant live - I am guessing the feed to the valve switch should
be connected to the output from the thermostat, and the other side of
the thermostat is connected to the output of the programmer?

Correct. The live feeds the timer and the valve SWITCH. The valve MOTOR
is fed via the thermostat from the timer OUTPUT. The SWITCH OUTPUT feeds
the boiler.