Momentary switch/trigger to turn on HW recirculation


Still new here, so apologies if this is somewhere in the forum (may not be using the right search terms)...

My problem : I own a tankless hot water heater, with built in recirculation pump. My options for HW recirculation are timed (inefficient), learning mode, where an algorithm predicts hot water usage and activates recirculation 1 hour prior (cool, but cannot predict "rogue" showers), and trigger based, where you can set up a button somewhere in the house and just press it 5 minutes before your shower.

I would like to use the button feature, and automate it wirelessly with a z-wave or zigbee module. I am wondering if someone solved this kind of problem before, and what are my best options for hardware.

Got a URL to the button/water heater? I'd imagine you'd be able to use a dry-contact relay (momentary at like 1s) to turn this on.

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Mine is tied to the light in the master bathroom shower.

And with the Hot Water plug part of Alexa, we can tell her to turn on the Hot Water anytime we want to do laundry, dishes...

Easy peasy

Dry contact is probably fine, the button looks like an old school doorbell button, probably just a momentary contact (page 2). Not sure of the voltage, but I would guess 24V or lower (they recommend 24gauge wire, and less than 328 ft wire length for the buttons).

Thanks Rick,

I thought of this too (light switch, or motion sensor), but I am worried that will not be enough time for the hot water to "cycle through". Plus I don't necessarily want to recirculate every time I turn on the lights. I do have a shower only light, that may work a bit better than the vanity lights as a trigger.


Look into a FortrezZ MIMOlite. It is a z-wave device with a dry contact relay that can be configured either as a latched relay or as a momentary relay. Lots of people configure it is a momentary relay to control a garage door opener. Comes with its own power supply.

Another choice is to make your own Hubitat controlled momentary switch as is described in these posts about a zigbee garage door opener.


Wow---I had no idea there was a jumper on that board to configure this! Thanks for sharing that. Not sure how I've looked over that over all these years...


You're welcome. I'm glad to repay a small amount of things you've done that I have benefitted from, esp. my LED light strip! The MIMOlite is versatile device. It also has inputs available.


Thanks aaiyar. The Mimolite looks quite flexible.

Just purchased a LFM-20 for my fireplace dry contact needs. It is much cheaper compared to the Mimolite, but I don't think it supports momentary function :(.

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You can add momentary function via Rule Machine.

Or via one of @asj's apps. His "when_on_then_off" app is ideally suited for this purpose.

Nice. Probably worth the trouble to save 35USD.

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Definitely. In Rule Machine, you can do it via a simple conditional:

IF LFM-20 is ON Off: LFM-20

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