Drayton MA1 Microswitch?

Hi

First post; sorry it's so long, just trying to provide all of the information as I've spent a while diagnosing the problem already. My current theory is a sticking microswitch in the 3 way valve. I'm hoping someone can tell me if I could be on the right lines and if so, what I need to buy to fix it.
The boiler has been running every day to provide hot water, so I don't think it's anything catastrophic...

I have a very old Trianco oil boiler. There is a room stat and in the airing cupboard there is a hot water tank, a British Gas branded controller,a Grundfos pump and a Drayton MA1 3 way valve.

The boiler, and the pump definitely work and the lever on the 3 way valve moves the way I'd expect when I operate the controller. The room stat was a Tado and that was my first thought - although I could hear the click and the readout said it was sending a call signal to the boiler. To be sure, I swapped out for a very basic thermostat and it seemed to work, but it was false hope. After the heating was turned off, it didn't come back on. When I attempt to turn just the heating on, the boiler doesn't fire and the circulation pump doesn't start.

I can make the heating come on by setting both heating and hot water on at the controller AND turning the tank stat up. The 3 way moves to M and the boiler fires and the circulation pump starts. If I turn the room stat down, the 3 way moves to W. If I then turn the room stat up, it moves to M (or H if the tank stat is at temperature) and the boiler continues running. During all of this, the circulation pump continues running as expected.

That's why I'm thinking that it's a sticking microswitch.

Have I missed anything else? And if I buy the actuator head, would that be the right part to change? (I'm not convinced I fancy taking it apart and soldering in just the microswitches I've bought from somewhere random on eBay).

Thanks for taking the time to read all of this.

Change the actuator. And with this unit, be prepared to do so every 18 months or so. It is worth looking at purchasing a complete valve with this model, as it is often cheaper than just the actuator, and just use the actuator.

Old thread but relevant info here as I almost replaced my MA1 head at £70 but instead found a simple fix that's potentially a root cause for lots of these failed units:

I had the same symptoms and indeed the microswitch wasn't correctly closing and putting live on the orange wire. Microswitch was prime suspect, but it actually hadn't failed at all. Looked to me like over time the PCB slot in the plastic casing has been worked wider and wider until the cam couldn't push the microswitch to the closed position (it just prodded the PCB over on the tilt instead).

I just shoved the PCB back over to the "right" side, dribbled some superglue into the slot and it's now back in service doing its thing...

zerokelvin said:

My current theory is a sticking microswitch in the 3 way valve.

Click to expand...

If it is the microswitch, then with a bit of effort the microswitches are cheap to source matching ones via ebay, but I would purchase a complete actuator, then work on repairing your present one as a standby for next time.