Honeywell V4073A motorised mid-position valve problem

[Hameed]

When the programmer is on for hot water and then central heating is selected to come on, the heating stays on regardless of where thermostat is set and even if programmer CH is de-selected, it carries on churning out heating unless I switch both to off on programmer. I suspect the motorised valve unit because when moving the lever between auto and manual on the valve box there is no spring resistance this is maybe stuck on open?

What can I do to free up the problem?

 

[MANDATE]

As you say sounds as though the valve is open to CH.
This could be the valve itself or the gearing inside the actuator head.
You should be able to remove the head off the valve spindle, then test spindle to see if its free to turn.
Whilst off you can try moving the lever again.
If the quadrant in the head has dropped back to HW which means the return spring has unwound the motor, then there will be resistance when you wind the motor forward using the lever.
Be aware that the grey wire in the head will still be 'live' when both HW and CH are not selected, so turn off the power if you dismantle the head to examine the gearing.

 

[Agile]

Need to remove head to see if stuck head or stuck paddle.

Tony