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Calling for heat issue... Works only when HW selected (Not CH only)

mikelewis
Community Member

Hi, I have a Nest system with Drayton MPV actuator.

Having problems when CH only is selected, I am not getting the call for heat to start the boiler. However, when HW is selected or both HW&CH the call for heat is there and boiler fires up fine.

MPV is moving how it should but suspect an issue there.

Anyone help with this please?

Thanks in advance, Mike

1 Recommended Answer

Yep it was the MPV actuator - looking at articles and commentary online there are microswitches and my guess is the heating one is u/s.

 

Thanks again for your help and speedy replies.

(UPDATED - opened the MPV actuator and the hot water microswitch has a definite click and the heating microswitch is spongey with no click - The offending item)

View Recommended Answer in original post

8 REPLIES 8

Frustratedddd
Community Member

Assuming I have this correct, you are saying when heat called from the stat the boiler does nothing?

You are UK?

Yes - Exactly that. HW off and CH called for heat from the stat - no boiler fire up. When HW on, stat on tank higher than temp - Boiler on. Boiler also fires if HW/CH on together with stats calling for heat.

 

and Yes - In UK.

OK, just one thing to prove first, call for heat on the stat and listen at the Heat Link to make sure you hear the relay click. Do it a couple of times just to confirm call and off. You might need help with one end obviously if to far away. That will prove your Heat Link is working.

My guess is a sticking valve if the Heat Link is working.

Thanks.

I've checked (using the app so could be right next to Heat Link and I hear a relay click on and off when I call for CH heat and stop. So it looks like the relay is working, 

 

The valve is not stuck, I can move the valve easily with actuator removed. 

 

One more thing with MPV actuator. When I call for HW it moves to the Water position. When I then call for CH heat, it moves to mid as expected. Then if I close the stat on the tank it moves to the Heating position as expected. Now, after I moved the tank stat and get the water to start again, it doesn't moved the MPV to the mid position, it stays on Heating. Then if I stop the call for heat from the CH, it moves back up to Water position. 

Could be the valve issue.

Very hard to solve if not on site, but does this help at all?

https://www.diynot.com/diy/threads/drayton-ma1-not-returning-under-spring-pressure-but.470727/

Hi, thanks again for your help.

 

I've had a read of that link. Have to say probably more amused by the banter than anything else, however it did highlight which wires on the MPV should be live at which time and I do get the correct grey and white wires live as per the post based on the condition. What I don't appear to be getting is the orange wire live (to pump/boiler) when I call for heat. All switching of live from the relay at the heat link box is fine so I am going to swap the MPV actuator and see how that goes.

 

Will write back with news once I've replaced it.

 

Thanks, Mike

Yep it was the MPV actuator - looking at articles and commentary online there are microswitches and my guess is the heating one is u/s.

 

Thanks again for your help and speedy replies.

(UPDATED - opened the MPV actuator and the hot water microswitch has a definite click and the heating microswitch is spongey with no click - The offending item)

That's that sorted, Great Job