TL;DR: How do I make the thermostat send a ‘heat’ request to the boiler without making the boiler use way too much gas?

Hi all,

I have a question about automating central heating. My current setup:

Ground floor:

  • Main thermostat linked to boiler (Honeywell T6 on WiFi through Honeywell integration)
  • One radiator with Sonoff TRV-ZB, zigbee
  • Three radiators with non-smart knobs that are usually open
  • The main room has a Sonoff Presence sensor

First floor:

  • Three rooms that can be occupied with Sonoff TRV-ZBs.
  • Two of three rooms have Sonoff Presence sensors

All rooms that can be heated smartly are controlled through a blueprint once shared here called ‘Advanced heating control V5’.

I have a helper called ‘Comfort Temp’ which is a slider that controls the setpoint on the main thermostat and the TRV of an occupied room.

So the obvious question is: is there any good way to get the main thermostat to send a heating request to the boiler?

I’ve seen something about a WiFi module that you can put in between the main thermostat and the boiler that offers more control (Nodo OpenTherm Gateway, OTGW). Does anyone have experience with this? Or do I solve this with more TRVs on my ground floor? I’ve heard about central heating systems not enjoying a fully thermostatic valved circuit. More TRVs also means I have to replace the valves on a couple of radiators.

Any advice would be greatly appreciated!

  • GreatAlbatross@feddit.ukMEnglish
    1·
    8 hours ago

    Boilers are kinda on/off, from a control perspective.
    The boiler heats water to the set flow temperature, pumps it around the loop, and repeats until it’s switched off.
    The amount of gas used is modulated by the boiler to make the water come out at the right flow temperature.
    Unless all the rooms in your house are perfectly insulated, or so badly insulated that they lose heat instantly, ad-hoq temperature changes in individual rooms is tricky to do well.

    I did have smart TRVs for a while, but actually ended up binning them.
    So my current solution is:
    HomeAssistant controlled call-for-heat. This is a relay that when connected, turns the boiler on.
    Temperature sensors in each room. This allowed me to balance the radiators so they all warmed up evenly, and also feed into the HA thermostat to decide when the heat needs to come on.
    Manual TRVs in each room set to slightly above the normal target temperature. So they’re normally open, but will close if something crazy happens, like someone turning on a fan heater.
    Timed target temperatures in HA. So the target temperature drops at bedtime, and rises just before I get up.

    I also lowered the flow temperature of the boiler, which improves efficiency.
    I’m not 100% sure what you’re trying to achieve in your setup.
    But adding TRVs to each room (and having one always-open, like the bathroom) would be a good step forward.