What an idiot!

I've bought a starter kit with smart room thermostat and bridge (successfully fitted) and some radiator thermostats. Being an idiot I didn't check that my existing thermostatic radiator valves were compatible with the tado ones and they're not - they're Pegler Mistral II. Will I need to have these replaced before I can install the tado smart valves? If so any suggestions as to what I should replace them with? Thanks

Best Answer

  • GrilledCheese2
    GrilledCheese2 ✭✭✭
    edited March 29 Answer ✓

    Yes, a heating system will need a bypass that prevents the water circuit from being fully closed. Historically this was done with a single radiator, but today it is done with an auto bypass valve. The valve is normally closed but opens when the TRVs close, due to the difference in water pressure. The auto bypass valve can be fitted on the pipework outside the boiler, or some boilers have an internal bypass.

    You may still need your bypass radiator. It depends how your heating system has been updated in recent years. Probably need a plumber to determine where your bypass is and whether you can have TRVs on all radiators.

    If you do fit a TRV in the same room as the wall thermostat then group the two together in the App. The TRV will be controlled by the wall thermostat to accurately regulate the temperature in the room.


  • Replace them with a TRV that has a M30 x 1.5mm thread. Personally I’d use Honeywell or Drayton, but it depends what is available in your region.

  • Thanks for the reply - looks like I'll need to spend some more money and get the TRVs changed to get the tado system fully up and running.

    Another question if you don't mind. The room where the wall thermostat is fitted has a radiator with no thermostatic valve so is permanently on when the heating is switched on. I assume this is some sort of by-pass system. Do I need to leave this as it is or can this be fitted with a TRV as well?