Drayton MA1 Mid-Position Actuator (CH/HW motorised valve)

[Customer]

I know nothing about central heating systems or their associated controls but I noticed that the boiler wasn't heating the water and so we've had to revert to the immersion heater to get hot water.

The three pipes connected to this Drayton MA1 motorised valve are all cold to the touch but the MA1 itself is quite hot if you touch it, which would suggest to me that there's some sort of electrical fault with it - maybe a failed motor?

Screwfix sell replacement motors @ £23.99 or the whole thing for just under £80 but is there any way to test first before I chuck my hard-earned at it?

[Theo]

There's usually a slider which you can use to move the valve manually. On this pic I think it's the one marked W-M-H:

When you slide that, you can feel the resistance from when the motor is engaged and when it isn't.

I'd try experimenting with that, with the motor both powered and unpowered, and see if you can tell if the motor is providing any force.

You can also set it to the hot water side (I'm guessing that's 'W' but maybe somebody plumbed it backwards) and confirm that the boiler does heat the water successfully, pointing to the valve being the problem. If manually setting 'W' gives you hot water and 'H' gives you heating (or vice versa) it points to the valve being a problem.

Although I think a mid position valve shouldn't have a closed position, so unless it's very broken I'd be suspecting the pump. If you move the valve manually and still neither of the pipes get hot, that starts to point more towards the pump (or upstream towards the boiler).

Theo

[Customer]

Thanks Theo, that's great.

[charles]

The motor is held on to the valve by two screws. Remove it and see if you can turn the valve. That should indicate whether it's the valve at fault.

[Customer]

Thanks Charles, much appreciated.

[Brian Gaff]

That sounds like a naff way to design a motorised valve, one might have imagined some kind of microswitch to cut the current at either end of travel. Brian

[SteveW]

Small synchronous motors have no problem with being stalled. It makes for a very simple design, with the motor moving the valve until it hits the end stop and returning back under the force of a spring when de-energised.

Cutting the power at the end of travel would required removal of the spring and a more complicated control, needing to power the motor back again when required.

[alan_m]

+1 A fairly simole design and if its good enough to be working in a million+ homes don't fix a design that isn't broken