CHtg pump running with actuator valve closed

My pump occasionally runs although all 3 actuators (2 zones + Hot water) are closed. Naturally its a bit noisy because its pumping against "blocked" pipes. I have checked the boiler overheat and overrun stats and they are not triggering. Boiler shuts down when actuators closed.

I disconnected all 3 actuator wires to pump+boiler and reconnected them one by one and this showed that one actuator ( 2 port spring return suspect Horstman only a few years old) was supplying volts even though it was closed, but not all the time.

Dismantled it: the cam which operates the microswitch was unworn and the microswitch contacts click normally. Switch mounting is secure.

I am tempted to replace the microswitch (actuator heads are expensive and this valve has been discontinued) but before I do, could this intermittent fault be caused by anything else?

sounds like the micro switch is stick on when the valve is shut.
if you still have voltage on the orange when valve shut.

the grey feeds the valve perm live.
so is micro switch stuck and valves shut the orange gets its live from the grey wire on.

Turn off power and disconnect grey & orange coming from valve at wiring centre. Test continuity across these two wires. open circuit, switch is ok. Close circuit, switch stuck.

Thanks for advice. There is voltage/continuity like you said but it is only occasionally.

Do these microswitches fail like this- I thought they lasted for at least 1,000,000 cycles. This has only done a fraction of that.

A related question please. On the Horstmann Z222XL 2 port spring return actuator (which has this suspect switch), how does the motor park itself when the valve is open, or does it keep pushing on against the stop all the time 240v is applied?

Some postings here //www.diynot.com/forums/viewtopic.php?t=8369
talk of diodes and resistors inside 3 port valves