I have a Google Nest thermostat, still working but I’m after local control, so…
At the moment its wi-fi is off, so it continues to use the last schedule it was programmed with. That cuts out Google but leaves no local control.
It seems to me that a thermostat is only a switch. Since I have a temperature sensor in every room (in the motion sensors) it ought to be relatively simple to turn the boiler on and off according to the temperature in rooms that are occupied.
So the questions are:
Is this a stupid idea?
Can the Nest thermostat be used as a local switch (I doubt it)?
What kind of switch should I be looking at? Zigbee for preference, but wi-fi would do.
I’m thinking of something like a smart light switch that can be turned on and off by Zigbee, but also manually.
Or am I going to kill myself?
For clarity… The motion sensors are Philips Hue - they provide regular temperature readings even when there is no movement.
Yes thermostat is just thermal switch.
And what you described as alternative is pretty common approach, not stupid idea.
One thing to keep in mind though is that whatever hardware you use, set it up a way it doesn’t purely relay on HA.
Use smart relay like Shelly 1 that can be programmed to turn boiler off after certain amount of time (or at certain time) even if HA is down.
you need to know what you are interfacing with. Your HVAC system does need a simple dry contact or it needs 24v/230v on the port that commands start and stop the heating/cooling?
as suggested do not rely on HA (or any other “hobbyist” automation tool for critical services) there are smart thermostats that can operate without internet, search based on your region/HVAC system, in this way your HVAC will run independendtly from HA but HA itself will be able to monitor and to do smart things like heating based on occupation or based on the forecasted weather - as long as you leave a fallback scenario on the thermostat -
if you ultimately decide to go for the smart switch route chose a device that can have its own internal schedule (like a Tasmota switch or a Shelly) so you will be able to have a “baseline” heating schedule but able to change it via HA
if using a smart switch do not reinvent the wheel there are hundreds of smart thermostat integrations, take a look at Better Thermostat
there is a way to “hack” (some??) Nest thermostat to avoid cloud interference, take a look here: Introduction - No Longer Evil
Thanks for the link. “No Longer Evil” looks really interesting, but unfortunately my thermostat is Gen 3, so not yet supported. I’ll keep an eye on it.
If you replace a thermostat with a simple smart switch, you must replicate the timing protections that the thermostat provides or you can damage the equipment.
No mention of the boiler make and model number, so no way of telling if it just uses the industry standard method of control, shorting 24vac to switch on, or some unique protocol.
Does your boiler have smarts to prevent quick oscillations of the contacts frying things? Fan motors and ignition lighters often do not appreciate being cycled on and off as your ultra sensitive thermostat hovers around two decimal places either side of your desired setting.
Hysteresis needs to be integrated into any HVAC climate control - a trap for new players. For some devices, this is on the boiler end. For others, the thermostat end. For others, the software that integrates them.
Yes, a climate control integration can be set up to use temperature and presence sensors from each room and make decisions on when to switch your boiler on and off. Yes it can drive a relay to do this, and if your boiler is compatible, it can control it successfully.
Whether you use an old Nest to do the switching or a cheap ESP8266 with a simple relay, the software will be an integral part of your search for a suitable solution.
Tell us what model your boiler is and maybe you will get further ideas.
Our family personally uses two Sensi ST55s because the local interface buttons are really good, and it has excellent HomeKit (mDNS) support in Home Assistant.
Oh yes, there’s smarts. Sensing for loss of gas and water, etc.
Refer page 27 for where to remove the link and connect your relay contacts to the Room stat/timer connector, and page 58 onwarda for integration. I note the necessity for regulatory installer certification in the manual too.
Any dry contact 10A (they are the usual ones you will encounter) SPST relay should be able to switch the boiler on by closing the contacts, and you can integrate that into your HomeAssistant Climate Control integration, along with temperature sensors as required. Note for fail safe if your integration control fails, the relay should stay off. The presence of a Neutral connection may indicate your wiring should be to 230volts grade, something most relay boards will support with screw connectors and suitable mains rated wiring. The whole boiler draws less than 3amps, so plenty of headroom with a switching 10amp relay to turn it on and off, and even a light switch with a switched relay rated for 3amps at 230volts could suffice. Be sure to adhere to wiring standard conventions for wire colour coding - the next service person that comes along’s life may depend on it.
Note: Your HomeAssistant controller replaces the switching functionality of the thermostat contacts, not switches the mains power to the entire boiler. The climate control integration mentioned by @inventor7777 provides the necessary hysteresis and other parameters necessary for home automation. The boiler controls any fans internally.
Good luck!
Bit touchy subject right now with the recent sad news about Hayden Panettiere. Not recommended.
