Extension kit

The extension kit can work as a switched live or low voltage digital ?

If it is in digital mode, what turns the pump on and opens the zone valves, is it performed by the boiler ?

My system is a normal S plan system and I know that I could use the extension system in relay mode but I want to use the digital control to better modulate the boiler, especially so it shuts down more elegantly rather than performing a crash stop when the timer switches off with the boiler at 100%

Ideas ?

Best Answer

  • GrilledCheese2
    GrilledCheese2 ✭✭✭
    Answer ✓

    @GaryC if your system is S plan you will need to replace the traditional wiring centre with a digital wiring centre to control the valves. For Vaillant their new VR66 wiring centre is not compatible with Tado, but their older VR65 wiring centre is meant to be compatible. Unfortunately the VR65 is discontinued, but you’ll find posts on this forum of people buying it second hand and getting it working. I also remember reading that someone was using a Glow Worm wiring centre with Vaillant and Tado. Glow Worm is a subsidiary of Vaillant.

    Others on this forum can probably help you, but you’ll have to give more specific information about your system.


  • The extension kit can work as a switched live or low voltage digital ? Probably not 'or'.

    If it is in digital mode, what turns the pump on and opens the zone valves, is it performed by the boiler ? In any modern boiler, the pump is powered from the boiler. The programmer controls the valves, so this will be the extension kit in Tado world.

    I don't think there is ever a crash stop (whatever that means) as the boiler is powered permanently and can makes its own decisions on what to do when demand for heat ceases.

    I've put in a request to Tado to start modulating my boiler and I'm awaiting their confirmation. I can't see it working if they ignore the SL. I think my WB boiler will expect SL plus digital signals, but will fire if it just has the former, not solely the latter.

  • My system is wired as a S Plan

    The timer applies power to the room stat and/or the tank stat.

    When either close, they apply power to their associated zone valve which opens. When a zone valve reaches fully open, it applies power to the pump and the boiler.

    The boiler powers up and sees a flow and temperature below its firing temp and fires. When the temperature of the return flow increases it modulates firing until such a point its warm enough and it shuts down, then fires intermittently to maintain temperature.

    If the time period ends, the timer removes power from the stats, this closes the zone valve which takes power from the pump and the boiler, so even if it was firing at 100%, it stops, no cool down, no purge, nothing.

    So, if I use the extension kit in switched live, it will just work the same, but if I put it in digital mode, I take it the tado would expect the boiler to start and stop the pump and open the relevant zone valve ?

    Or would I have to put in relays from the volt free contact to switch the pump and zone valve and make the boiler permanently powered up ?

    House was only built in 2002 so its not an 'ancient' system but it is a more traditional one.

  • That’s pretty standard S plan then, just not the modern boiler version. It’s all hanging off a switched live.

    I’m waiting for a further response from Tado as their first reply didn’t match my set up.

    As I said before the digital connection can’t be at the loss of the switched live or dry contacts. I’m expecting both sides of the extension kit to work. One end will still be able to energise the valves and the other end will tell the boiler to modulate.

    I’ve wired in the control cable. I’m waiting for more comms, but there’s nothing stopping me reconfiguring and seeing what happens.

    What digital bus does your boiler support?

  • Its meant to be ebus but there are mixed messages about the Vailant compatibility with Tado so it might all be an non starter anyway.

  • Ah, I see

    The VR65/66 does all the required switching and the boiler would need to be setup to use it (and, yes I see the 66 does not work with Tado)

    Sounds like a non starter really which is a real shame.

    I know I could just use the extension kit in switched live mode, but that really doesn't give me any more than I have now

    Shame it can't work in a 'hybrid' mode.

  • Unfortunately many of the boiler manufacturers are using proprietary interfaces to restrict the use of third party controls. It’s an issue for many of the smart thermostat manufacturers. I think Tado has done better than most in trying to support these digital interfaces, but there’s a limit to what they can achieve.

  • Doesn't it all seem very messy.

    Tado support digital bus, but they might not quite have the specific flavour of digital bus we need (as manufacturers are free to change).

    Where Tado support digital bus, they apparently drop support for switched live when in digital mode. This leaves the S plan users scrabbling for a solution to switch the valves and also to ignore (override) digital bus messages during HW cycles. I think Tado should sort this bit, as it's all possible in the extension kit.