Motorised valve problem

23 Apr 2012
Reaction score
United Kingdom
Gas CH and HW system, with a Drayton MA1 3 port motorised mid position valve. Potterton Suprima HE. System is 5 years old and works well but have suddenly got a problem. I HAVE TODAY REPLACED THE ACTUATOR MOTOR but still have the following problem whether the actuator is on or off the valve:

1 With HW cylinder stat set to off, I turn up the CH stat for heat and boiler & fan (warm air system) start and the actuator lever is at the 'H' position - so far so good.
2 Turn HW cylinder stat to 50°+ CH still on and the actuator lever moves to mid position 'M' as it should do BUT the unit clicks about once a second and the lever moves very slightly back and forth. Even if I remove the actuator from the valve this still happens. With the actuator off the valve, if I move the black auto lever to the far right or left, the clicking stops and I can hear the motor move slightly.
3 With HW cylinder stat still at 50° and CH stat turned down low, CH fan does not switch off as it should and actuator continues to click at the 'M' position instead of moving to ‘W’. So this is a fault but where?
4 Turn CH stat so the fan should be off, turn HW cylinder stat down low and boiler goes off and actuator lever moves to 'W' even when unit is on the valve - so valve itself seems OK.
5 Turn HW cylinder stat back to 50° and system reverts to 2 above and the actuator lever moves from ‘W’ to the ‘M’.
6 Turn HW cylinder stat off and system reverts to 1 above when CH stat clicks on.

Until I can get it sorted, I am running the system with the HW cylinder stat off and using the immersion heater.

Any thoughts or suggestions would be really welcome.
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Don't know if you can replace the actuator head on that valve, if you can then I would replace it.
Actuator heads have a geared quadrant, they also have two micro switches where contacts either don't make when they should or don't break when they should. There is also a small printed circuit board producing a modified voltage to hold the valve in mid position against the strength of the return spring.
I think the problem would be solved with a replacement head.
There is lots of information on mid position valves on here and I'm sure your problem has cropped up before.
Try search using 'mid position drop back'

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