How do radiator smart valves interact with thermostat

Apologies if this has been asked before, I wasnt sure exactly how to word a search. In this scenario: ambient temperature 18, Smart thermostat setting 15 (ie it would be switching boiler off) radiator smart valve setting 20, would the radiator valve setting override the thermostat and cause the boiler to switch on? Or will the boiler only switch on if the thermostat setting is above ambient?


  • eezytiger
    edited October 12

    I installed Tado last week, with seven SRTs and a smart wired thermostat connected to my combi boiler via eBus. With this setup, if an SRT requires heat then the smart thermostat should (and does) turn the boiler on, even though the smart thermostat itself does not require heat.

    While this is great, it might require some tinkering with the lock shield valve for the radiator for which the smart thermostat acts as a room thermostat, because my hallway (where the smart thermostat resides) has been getting overheated due to heat requests from other rooms forcing hot water through it when the hall itself is fully up to temperature. I'm getting there with my adjustments, but still fine tuning.

  • cbd20
    cbd20 ✭✭✭
    @IanK both options are true depending on how you choose to configure the system.

    For each room you can specify the "zone controller" as either the smart thermostat (or whatever is wired to your boiler) or "independent".

    If a zone controller is set, then the smart radiator thermostat (SRT) in that room can request that the zone controller (in your example the smart thermostat) fire the boiler. This way every room can request heat as and when required.

    If no zone controller is set (so the room is independent), then the SRT will open if it detects the temperature drop below its setting, but it cannot request the boiler to be fired. In this situation, it would require the smart thermostat to actively be calling for heat too in order for that room to heat up.

    You can mix and match setups across rooms if you wish.

    @eezytiger in your case, provided you've got another radiator without a trv of any kind (e.g a towel radiator) and/or your boiler has an automatic bypass fitted, then you could fit a smart radiator thermostat to your hall radiator too. That way, this would close if the hall wasn't requesting heat and you wouldn't get the overheating problem you see.
  • @IanK Yes, that definitely crossed my mind, but all my SRTs (seven out of nine rads) replaced old manual valves with a straight swap and no plumbing skills required. The hall radiator never had a TRV fitted, relying on the room thermostat for control, and I'd need a plumber to sort it for me as I don't do plumbing. I do have a mate that does, however. 😁 But I think I can get there with a bit more manual tweaking without spending further. I'm nearly there now in any case.

    I appreciate the thought though. Thanks. 👍

    p.s. The bathroom does have a large towel rail/rad which is manually left fully open, so if I need to add one more SRT for the hall it's definitely doable. I just hope nobody ever closes off the valves if I do.

  • Usually (but not always) the radiator left without a TRV is in the same location as the wall thermostat which in turn is located in potentially the coldest room of the house.

    What you may find is that as we move further into winter and the temperature drops (it has been pretty mild so far!) that the overheating lessens or maybe disappears causing the reverse issue! This would be caused by other rooms heating up faster and reaching temperature which would shut off the boiler before the main thermostat has reached temperature.

    Lots more room / time for tweaking things - its half the fun (but don't tell the wife!)