Junkers Euroline ZS 23-1 compatibility

Hello, I have Junkers Euroline gas boiler and Siemens RDE 10.1 termostat. I wonder if I can replace it with tado wired thermostat. Thanks!

Best Answers

  • luteijn
    luteijn ✭✭✭
    Answer ✓
    Looks like it's just a simple relay so should work. Q12 / brown is probably 'live' and Q14 / blue switched live, at least then one of the colors is standard... It doesn't really make much difference how they are wired anyway, you'd just stick one on tado's COMM and the other on NO. If the brown wire is indeed live, then I'd put that on COMM...
  • johnnyp78
    johnnyp78 ✭✭✭
    edited December 2022 Answer ✓
    Tado thermostats are designed to take either voltage, you’ll be fine with both. Follow @luteijn ’s instructions.


  • Hi @luteijn! thanks for comment. Are you sure I won't kill the thermostat? I have no idea weather the wiring is 230V or 24V. Since you say 'probably' I would rather double check :) Thanks anyway.

  • It will be fine. If you really worry, you could add a fuse e.g. 230V 1A in series with the relay, or an old-fashioned lightbulb as a current limiter, but that would arguably be less safe as it is more of a hack.

    The tado relay can handle up to 230 V at 3 A, so looks like the Siemens has a slightly bigger margin of 250 by 5, so I can't guarantee anything, the old system could be pulling 1000W through the thermostat. But, since you're controlling a gas boiler, not some sort of electrical heater with the primary power going through the switch (which would be a pretty dumb, but straight-forward/cheap design), even if the current you're switching is directly powering pumps, gas valves and sparky bits, it should not be 3A. And it probably wouldn't be doing all that: by completing this circuit, you're just giving the boiler a (strong) hint that you want some heat, please. It has its own logic on board to decide what to do with this demand.

    Often these boilers are on a 3A fuse at their connection to the mains, so they wouldn't have more than roughly 700W of total electrical budget. It gets it energy mainly from the fuel, not from the mains, that would be cheating.

    So, just replace the siemens 1-on-1 with the tado, it will work.