Zigbee Dry Contact Switch UK for Boiler

I currently have a Nest Thermostat controlling the heating but I am looking at moving over to some sort of TRV setup and controlling the boiler via HA.

The call for heat is just a no voltage switch which in theory should be simple to replace but I cannot find a Zigbee product that does the job. I have seen that lots of door sensors can be hacked to do the job but ideally I would want this to be mains powered to give a little more resilience and keep the heating working.

Everything I have seen is either wifi, live contacts, involve soldering PCBS or one had £50 shipping to UK for a £20 switch…

Failing that is there a way I can get the Nest Link to do the triggering via Zigbee (wasn’t sure whether I could add a switch into the currently unused thermostat wiring but I think that is 12V so I guess that is still an issue)

Normal is to use “contactor” for switching high-load products such as heating (boilers/heat-pumps), and electric motors. The contactor itself is controlled can be controlled with any mains-powered smart switch

https://en.wikipedia.org/wiki/Contactor

https://www.c3controls.com/white-paper/basics-of-contactors/

Examples of contactors are ABB ESB25-40N-06, Iskra IKA232-20, and Siemens 5TT58300

https://new.abb.com/products/1SAE231111M0640/esb25-40n-06-installation-contactor

https://mall.industry.siemens.com/mall/sv/se/Catalog/Product/5TT5830-0

https://www.iskra.eu/f/docs/61693/Installation_contactors_ver3.0.pdf

The circuit doesn’t actually switch the boiler but controls the contactor inside the boiler which does. I believe the circuit is either 12v or 24v with very little current and when the circuit is made (thermostat is triggered) the boiler is fired up.

My concern with a lot of smart switches (designed for lights) is that they look to be passing through voltage to the switch

Is there any reason you only want to use ZigBee ? The esp01 WiFi relay board with esphome would only be ÂŁ2 ish. I use several of these and they work fine for dry contact applications

No probably not. I have always found WiFi devices are less stable (partly in implementation and partly just WiFi itself) but this is probably just my preconceptions.

Will check them out

I have over 80 WiFi HA devices and they hardly ever cause me a headache. Unlike ZigBee that drop connections regularly for me so have replaced any I can with WiFi. Mostly battery sensors remain.

Btw I do have 2 APs across the house for the HA devices.

That is exactly why you want to to use an external contactor as I suggested. They are electrically isolated.

Hi @jampez77 I have the same challenge.
How did you solve the problem?

I’m assuming this was meant for @jameson_uk ?

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In case you end with out of options, and consider wifi defices again then Shelly1 has dry contacts while the device itself can be powered by 230V AC.

Another option is shelly UNI. it can be powered by wide range of DC, at the same time it has potential free relays (no try contacts though)

I was looking again last week but there doesn’t seem to be a nice Zigbee solution. I have seen people rewiring SONOFF controllers and a few hacks or custom builds but nothing off the shelf.

I am currently just bodging the nest controller by setting the heating right up when I want it on. It is working by virtue of the TRV settings so the kitchen where the thermostat is doesn’t get much warmer but the rooms that are still cold get heated. I will look again at some point but the WiFi options switches are the only ones that will work and I am still very wary of WiFi IOT stuff in terms of security and privacy

Thank you for the update.
I think I am going to try a two part solution…

A solid state relay, to do the dry contact switch…
240V-Mains-Relay
Then any zigbee or wifi switch to control that, such as…
BSEED Smart Switch Remote Control DIY Wireless WiFi

if you have already Zigbee, better take a Zigbee relay, e.g. the zbmini

Interestingly, this just came up for me on Amazon

which still would need something to house it but it seems to be the closest I have come across.

Might take a punt on one anyway so I can see if it would do the job if I ever do replace the Nest

If youre not in a great rush, its a lot cheaper on Aliexpress:

They do one in a case too

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I am always wary of Aliexpress… It looks great when you click through and it says £4.24 but that is only for the remote fob. The board is £10.39 which is still quite a lot cheaper than the £18.87 on Amazon.

The case does look interesting however it doesn’t actually allow you to use the USB power socket so I would need an additional transformer too. Also way (having been stung like this before on Aliexpress) whether you are actually getting the case and board or just the case…

Might do a bit more digging on Aliexpress and see if there are other ones with cases that actually fit the USB (although I suspect they will all be the same as this one)