"M" terminal always live?

Hi there,

I have a Rachio Gen 2 controller, I recently purchased a pump to begin using irrigation water from a lake instead of using the city water supply. When I went to hook up my “M” terminal to the pump start relay I discovered the “M” terminal is on and supplying 28 volts at all times. Is this normal?

I would imagine that this terminal should not be live until a given zone is activated and water is required? In addition to this, once I hook everything up, the Rachio turns itself off leading me to think I’ve wired something incorrectly, however I’ve checked every connection and it seems like I’ve hooked everything up right. I’ve reached out to Rachio on Wednesday with no reply as of yet, I’m hoping someone can assist.

Thanks so much!


Picture of your instal?

Are you measuring AC or DC voltage? Are you still using an original Rachio power supply?

Another question is relative to what terminal are you measuring the voltage? M terminal may appear live relative to 24V- terminal (SC on the older devices) while being “off” relative to commons.

I’m with @tmcgahey, pictures are worth a thousand words, but answers to above questions will come in handy as well :wink:


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Here are some pictures. The wires I have been hooking up are disconnected but are hooked up to C and M. I am measuring AC voltage.

To me, this looks like a blown MOV, you can probably fix it yourself, or have Rachio replace it (in case your controller is still under warranty). MOV is a protection device, it prevents surges from damaging a more sensitive devices (like transistors), when surge damages such a component, they usually cause a short, which is what you are seeing here. Blown MOVs usually show some sort of visible indication that something went wrong, in case you, or someone you know, is handy with a soldering iron, this is a 5 minute fix.

Bigger question would be what caused a surge to begin with, what kind of pump relay do you use within the hunter housing?

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Thanks Gene! That’s very informative. I do believe my Rachio is under warranty. I used city water supply last year and just moved to a pump so I’m un-sure how long it’s been this way. For all I know it could have come from Rachio this way.

I am just using the standard Hunter pump start relay. Nothing fancy or custom.

I guess I will start with Rachio and see where it leads me.

Hi Gene,

Just wondering if you could point me in the direction of what I might be looking for here? I’ve got the board out, nothing appears burnt out or the like.


I agree, nothing jumps out as outright wrong. The board looks good.

Try powering on the board as it sits and doing the AC voltage measurement between M terminal and Commons. Are you still seeing 24V+?

Can you also please take a photo of the other side of the board? Seems Rachio have updated the design from the last version I’ve looked at. R79 is new and so is D18. Trying to wrap my head around the purpose of the new circuit. At a first glance, this is a current sense circuit, dedicated to M terminal, but using a diode on an AC circuit is…

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