Hot water controls not working Baxi Boiler


I have a Baxi Duo-Tec Compact+ 1.24 GA boiler. Per the advice from Tado, I replaced my existing wired thermostat with a Tado Wired Thermostat V3 (EU purchased).

Radiators work great. The Radiator head I added to a back room calls for heat appropriately.

However, I have no hot water. The system shows hot water on but never actually fires the hot water. I have a tank attached to the boiler. The boiler control panel will properly read the temperature of the instant and tanked water (both cold over time ...). It doesn't show the proper hot water temp setting. For example, it will show 55 when I have 60 in the Tado app.

Disconnecting my thermostat by removing it from its backplate will cause the boiler to immediately fire and make the water in the tank hot.

Tado support has so far only decided to refer my situation to level 2 support.

Has anyone run into this?


  • Is your boiler a combi with an integral hot water cylinder? And do you know how the Tado thermostat is wired to it?
  • Valaki1234
    edited December 2022


    I have a similar boiler, Baxi Luna Duo-tec 1.24 E, for me both controlling the heating and DHW work fine.

    When I connected the Tado thermostat to the boiler via OpenTherm (I assume you also use that and not the simple relay), I needed to change what OpenTherm protocol variant the boiler should expect: the "Baxi" OpenTherm or the standard OpenTherm. The default setting on my boiler was basically "auto-detect", however I noticed it does not work and needed to change a parameter so the boiler expects "standard OpenTherm" only. Maybe you should give it a try.

  • @johnnyp78 it is a combo boiler and there is a tank sitting below it. As I understand it the boiler has a sensor in the tank and will keep it warm by recycling the water. If the tank runs low it can top it off with more instant hot water. I bought the flat like this and don’t know the history of the decision process.

    I wired in the thermostat per the instructions. It is two wires, + and -. They are interchangeable per Tado.

    Pics of the original and new wiring. I can’t seem to do uploads on mobile :(.



    Thank you.
  • @Valaki1234 was this change on your boiler? I noticed my has a P setting for opentherm but there isn’t guidance for changing it. How did you do it? Thank you.
  • Did your old thermostat communicate with your boiler via OpenTherm, or only via relay connection (On/Off) ?

  • bex
    edited December 2022
    @Valaki1234 i can’t be sure, but the old thermostat was supposedly modulating and controlled the hot water. It was from Baxi. The RC 014 iirc.
  • @Valaki1234 doing a bit more reading, changing the Open Therm setting makes sense. Unhelpfully, my manual says P67 manages Open Therm and 00 is auto-detect. It says I need to see the Service manual for other options. So far I’ve been unable to find one online. Did you?
  • I have found that document from the Czech Baxi site, unfortunately not in English:

    What you need to do:
    1. Go to the P22 parameter and set it to value 22, this will enable lots of by default hidden parameters
    2. Go to P67 and set it to value 02. (with this you force the boiler to only understand the standard OpenTherm)
  • @Valaki1234 děkuji moc. This is a chance to make my boiler better and practice my Czech :). I’ll update in a few days as messing with the boiler now is an unwise plan.
  • @Valaki1234 for clarity, you’ve got the Tado set to 01 Open therm and not D62 for Baxi?
  • @bex : On Tado side I ran the automatic setup via the "Tado pro" app, did not change the parameters on the thermostat manually.

  • Following up. Thank you @Valaki1234 your guidance was perfect. I set my boiler to use Open Therm instead of auto-detecting and it is working.

    After I did this, Tado finally got back to me and implied but would not confirm this was the right thing to do.
  • For future reference: what is written above ... works. I did the following to make my Baxi Luna Duo-Tec E 24 combi boiler to work with Tado Wired thermostat using OpenTherm protocol. (Switching from legacy relay operation)

    • Wire Tado thermostat as per professional installation instructions: (+) and (-) connections.
    • Choose OpenTherm as communication protocol in the Tado thermostat (D01 if I'm not mistaken - but surely NOT D62). Also activate HW (hot water) option.
    • Rewire the boiler from the M1 1-2 connections to M2 1-2 connections.
    • Activate extra options in the boiler by setting P22 to 22.
    • Choose OpenTherm communication in the boiler by setting P67 to 02.

    Now everything works fine. Even hot water control.