Mid-position actuator replacement

[Grenage]

I tested the heating yesterday and it was fine, but this morning I noticed that the house was warm and the heating was turned off. The thermostat stayed illuminated and heating carried on regardless of the temperature.

The MPV was stuck at heating; I killed the power and it stayed there, but I was able to manually move it across to hot water. All working as intended for now.

Since I was able to move the lever with relative ease, I'm guessing that the actuator has had its day. How compatible are different brands? It's currently got an ACL actuator:

View media item 102037
There are no isolators either side of the valve, so it would make my life easier if I can just replace the head.

 

[AndyPRK]

drayton or the blue british gas ones should fit straight on.

It maybe worth opening to see if the spring mount has broken off (plastic)
with the power off to the boiler. (switch next to timer/boiler)

 

[Grenage]

That was a damn fast reply.

Thanks, Andy; I can't perceive any obvious way to remove the head, but there must be a way. I'll have to set some time aside at the weekend. Shan't shell out for a new one just yet.

 

[AndyPRK]

It’s one of the black tabs.

Just press it in and wiggle a little

 

[Grenage]

Cheers!

 

[SimonH2]

It is often just the motor that's failed - they are a lot cheaper than a full head, and plumbers merchants will have them on the shelf. One of the known drawbacks of these valves is that they can be left for long periods with the motor stalled in the actuated position - which gets them warm. When the bearing lubricant is getting "a bit sticky" (which the temperature will accelerate), the gearing amplifies the torque to such an extent that the spring can't pull the actuator back.

 

[Grenage]

Thanks Simon; it's this the kind of thing you're talking about?

https://www.screwfix.com/p/drayton-synchronous-motor/28670

 

[SimonH2]

Yes, that's the jobby. First I would suggest switch off the power to the heating, remove the actuator head from the valve (press in the release tab and it should pull off), remove the cover, and then unscrew the motor - see if the mechanism moves freely then. Then try turning the little gear sticking out of the motor - you should be able to turn it with your fingers.
If the mechanism now runs freely, and the motor is hard to turn, then try a new motor first - it's a LOT cheaper than buying a new actuator head, and less connections as well.
Also, while the actuator is off the valve, check that the valve spindle moved freely - it's not unknown for the spindle to get tight and then the actuator spring doesn't have enough strength to move it.

 

[Grenage]

Brilliant, thank you. I shall let you know how I get on.

 

[Grenage]

Well this old model doesn't clip off, and it was mounted facing a wall so it was a bit of a bigger.

I managed to remove the motor and it all seemed to turn ok, I swapped the motor anyhow because £20 was worth not going through that again.

Unfortunately while it moved to heating, it only comes back half way when the heating is off. The springs are ok and the motor is new, so the valve must be a little too sticky for the retention.

The valve has no isolators, and I'm so busy at the moment that I think I'll have to get a professional in to replace it.

It was worth a go, and thanks for your help guys.