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thermostat suitable for Home Asistant (mander.xyz)
submitted 1 year ago by to c/homeassistant@lemmy.world
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Another noob question: see the attached image of my thermostat. Would it be possible to switch it for a smart one? What would I have to check? If it is possible, what would you recommend? If is don't want any 3rd party app or account?

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[–] 1 point 1 year ago (3 children)

Despite the name it’s not a simple on/off that can be done with a relay. Those 2 wires also provide power to the thermostat unit. I’d first try to find more information about how these thermostats report demand to the boiler before using a relay.

I’ve also seen someone that simply replaced the NTC/PTC on their existing thermostat with some ESP circuit so they basically controlled what the thermostat “sees”. Want more heat? Tell the thermostat that it’s 5℃ in the room. Want the boiler to stop? Simulate a cozy 30℃.

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  • [–] 1 point 1 year ago (2 children)

    The power being provided to the unit is just a side effect. More than likely 24vdc and a set of contacts. If you were to wire a simple toggle switch in and flip it on the heat would turn on.

    I've dealt with hundreds of thermostats they all work in a similar fashion the new ones just use multiple relays with a single power wire. The old school thermostats just used bimetal contacts or clock springs with a mercury relay. Modern ones use electromechanical or solid state relays. This includes things like the nest thermostats.

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  • [–] 1 point 1 year ago (1 child)

    The Junkers boiler at my previous place had an emergency mode where it was heating when the contacts were open. Even their simplest thermostats put a load on the wires depending on how much heat is required - so it doesn't go full blast when you are only slightly under the target temperature.

    So, this all depends on your specific boiler. While it might work with a simple relay, it might be far from optimal in terms of energy efficiency and wear&tear of the boiler.

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  • [–] 1 point 1 year ago

    Maybe that's a thing where you area at then. I've worked with heating units that have a simple temp probe and a manual dial that I converted to be "smart" by taking the outdoor temperature into account and then ramp the supply temperature up as the outdoor temp went down. This was a system that supplied hot water to radiators in an apartment building that was converted from a hotel. We replaced a pair of steam engine sized steam boilers to a direct fire hot water system by replacing the steam to water heat exchanger.

    EVERY system I've worked on was the same, short the wires and it turns on. Anything beyond that is controlled by the heating unit. A simple thermostat just puts in the call by allowing the power to flow. When a system had multiple wires i.e. Heat and Cool plus fan you have 4 or more wires depending on the system capabilities. One supplies power or ground the others control fan, heat, or cool by being shorted to the power or ground wire. Sometimes there are multiple stages that are controlled by the thermostat sometimes they are controlled by the HVAC units built in controller. But MILLIONS of homes and businesses in the US work in a similar fashion and even without a thermostat installed a tech can short the needed wires and make them work.

    https://home.howstuffworks.com/home-thermostat.htm

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