Battery operated thermostat with dry contact

Dear Community,

I'm looking for a thermostat that can be controlled by HE (Z-wave or zigbee), battery operated and has a dry contact to control my gas heater (simple 2 wire, 220V AC).

I found Tado which is promising (battery operated, dry-contact), but I don't know whether it can be controlled directly by HE, or only by including the Tado bridge and use an app to control the thermostat via the bridge.

I do not want any other device, just a simple battery operated thermostat, that I can manage in HE.
I want to keep the system operable without the HE too, so if anyone sets the thermostat by hand, that should be able to initiate the heating directly (not via wireless communication to a dry-contact relay.

Can anyone suggest such thing?

Thank you in advance.


My Centralite pearl thermostat is battery powered and uses two wires to control my natural gas boiler. Pairs to the hub with Zigbee, and can still be controlled manually at the physical thermostat.

You can use a GoControl or a Honeywell Pro T6 Pro z-wave. Sinope makes some great zigbee thermostats that will work too.

Yeah, I read about centralite, but it is mainly designed for HVAC system control on low voltage. I don't think it has a NO dry contact that handles 220V AC.

Ah you might be right. Not sure if it can do a totally dry contact. My system uses 24VAC. The settings menu is fairly extensive, maybe there’s a manual online that clarifies.

The Honeywell T6 Pro is a mains powered device and does not have z-wave or zigbee, but wifi.

Unfortunately, as look really cool.

Even your heater is using lv for control if it's whole house. (Or is this some type of space heater?) Your internal board still has to comply. The relays are done inside the unit (even really old ones) You use w for heat call and g for fan.... If it's just an on/off heater, you may have to go to a floor heater thermostat.

The Honeywell T6 Pro Z-wave.... I have one, fantastic unit.


Checking. I was reading the Honeywell Lyric T6, my mistake.

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It's funny, reading the bad reviews on the Honeywell site for it. Almost all of them are because it wasn't connecting to the internet (People not understanding the difference between Z-wave and wifi)

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Unfortunately, the T6 Pro Z-wave does not have a dry contact relay.

It is ridiculous how complicated it is to find a simple thermostat with zigbee/z-wave and dry contact relay


I've spent 1,5 hours on Google to find one, and after that I decided to be wise and ask for some help.


I don't think a battery powered device exists that has a dry contact relay.. The standard type relays consume energy when activated..

Won't a mains powered thermostat work for your use case?

EDIT: actually there are battery powered wall thermostats - like this. (unfortunately a WiFi model)

Correct. In your situation, I would suggest pairing a thermostat with a dry-contact 220V NO relay, with a low DC voltage coil.

Connect the relay coil to the R & W terminals of the thermostat. When the thermostat closes R & W, it will close the relay terminals powering your 220V heater. When the room reaches the desired temperature, R & W will be open on the thermostat, thereby also opening the relay.


If you decide to go with a mains powered thermostat (you need to pull wires to the thermostat for the gas heater, anyway), then I can recommend this one:

You can choose between 3A or 16A dry contacts relay, it keeps working offline to HE, the heating setpoint can be changed both by HE and locally, and even seems to have some kind of PID control algorithm implemented in the firmware.

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Yepp, the ME 81H.31 version has one 3A rated potential free contact. That would work, but I'd need to replace an old 2-wire battery operated thermostat, and it is already wired. Unfortunately with 2 wires only. So I can not supply the thermostat with any sort of voltages.

I wonder if a c-wire kit would help with that.

The upper right would be my wiring. However I only found WIFI versions on sale from the 81H.31

c-wire system is a low voltage system, so no.

In my case I have 2 wires. One has 220V live (so if you touch it, you die), the other one has nothing in it.

If you connect the live to the "nothing", then that cable will be 220V live also, and the gas boiler starts. It is that simple. So I don't even have neutral line there, only the live.

This is why I need a dry contact (potential free) to connect the two lines if heating is needed.

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Ok so it is just on/off. I think then using a step down transformer (220>24) branched off to the C wire of the thermostat might be your best bet.... (I've touched 220, you won't die but damned if it doesn't hurt... ack!)