Is the Drayton MA1 valve new? I ask since these are one of the most unreliable zone valves on the market. They typically fail with random problems that you describe.
Forget trying to diagnose them with a multimeter...there are too many failure modes.
The site listed gives a good summary of the issues. I suggest you unclip the white actuator and carry out a few checks yourself. Ensure the heating system is isolated from the mains power.
Check the spindle on the brass valve body is free to rotate by hand and there is no water leakage. The spindle will only move perhaps 15 degrees.
Remove the single screw on the actuator and unclip the cover. Check both springs are secure..it is common for the plastic posts to shear off.
The micro switches and other components can also fail but you can't readily test those.
It is often better to substitute a new actuator/valve to be sure.
http://www.seered.co.uk/drayton.htm
Forget trying to diagnose them with a multimeter...there are too many failure modes.
The site listed gives a good summary of the issues. I suggest you unclip the white actuator and carry out a few checks yourself. Ensure the heating system is isolated from the mains power.
Check the spindle on the brass valve body is free to rotate by hand and there is no water leakage. The spindle will only move perhaps 15 degrees.
Remove the single screw on the actuator and unclip the cover. Check both springs are secure..it is common for the plastic posts to shear off.
The micro switches and other components can also fail but you can't readily test those.
It is often better to substitute a new actuator/valve to be sure.
http://www.seered.co.uk/drayton.htm