Currently using Nest Thermostat just to turn heating on and off. Is there a better alternative device to achieve this?

Hello all,

I added sonoff trvzb’s to almost of all of our radiators a few months back. I’ve got them hooked into HA via Zigbee2MQTT alongside a bunch of snzb-02d’s thermostats and snzb-03 motion sensors and I’ve been playing around with the configuration ever since(!)

I’m in the UK and have a system boiler heating 2 zoned circuits + an unvented cylinder, all of which is controlled by 2x Nest Thermostats.

I’m using HA automations and scripts to toggle the trvzb’s on and off according to demand but underlying it all, I have the HA Nest integration calling for heat by toggling the hvac mode of nest thermostats from ‘off’ to ‘heat’ and back again. The trouble with this is that the Nest Integration stops working after about 24 hours and I have to manually restart it or it loses its connection to the thermostats.

So, as the thermostats are only being used as crude switches, I wonder if there is a simpler way to ask the boiler for heat? All the clever stuff is now sitting between HA and the various zigbee devices so there really isnt anything else for the Nests to do other than switch the boiler on and off.

But unfortunately, its at this point that I completely run out of experience & talent and so I have no idea if there is such a device or even if I’m thinking along the right or even achievable lines…

Has anyone out there had any experience of a similar situation that they could share?

Many thanks!

Depending on the exact make & model of your boiler, the “call for heat” signal to the boiler could be as simple as a relay - Either switching live 240Vac, or a low/no volt contact. A basic zigbee relay could replace the Nest device without any loss of functionality. If you need a no-volt contact, the relay would need modifying to ensure mains voltage is not sent to the boiler.
If you have a modern boiler that supports OpenTherm or similar, you could implement a PID controller and take advantage of adjustable flow temperatures - This could boost your efficiency by a few points.

Thanks Paul, it is a relatively recent worcester boiler but I’m pretty sure it doesn’t support opentherm, has something proprietary instead (another decision I wouldnt have made had I been aware at the time!). I’ll investigate the relay option. Cheers!

Worcester Bosch uses something they call EMS.
Like OpenTherm, there is an open source project that allows you to talk to the boiler. Have a look at https://emsesp.org/ - I’ve not used it myself, but there is no reason why you shouldn’t at least get basic control if your boiler is recent enough.
If not, I’m fairly certain WB will use a no-volt input to call for heat (so no connecting it to 240V unless you want to release the magic smoke).