Yes another Vaillant boiler wiring question :)

edited February 19 in Getting started

Hi All,

sorry to add to the large list of posts about Vaillant boilers.

So I have my tado (v3+) wired room thermostat connected direct to my Vaillant ecoTEC plus 837.

All working fine on/off does what it needs to do but its just relay mode (I think thats what its called), was hoping to get some intelligence into the boiler by hooking it up to the bus.

Am I right in that its just a case of plugging the existing wires into the + & - on the boilers bus ports, then on the tado backplate connect the two wires to the + & - on the right side of the backplate, then changing the mode to D07 on the thermostat itself?

I have seen posts about bridging but I can’t figure out if this is needed purely if using the extension kit or not. I don’t have the extension kit. Some people do the bridging on the 230V side, some on the 24V side.

attached is some pictures of how it looks currently (and working in relay mode) to help (hopefully).

Thanks in advance for any help that can be provided.

Best Answers

  • Montage
    Montage ✭✭
    Answer ✓

    Connect the ebus, find the boiler does or doesn’t fire on heat demand. If not, bridge the mains or low voltage to suit your preference.

  • Montage
    Montage ✭✭
    Answer ✓

    One is on and the other is on.

    I’m old school and I’d loop the mains level one.

  • BauBau
    Answer ✓
    Hello. The power supply to the boiler plate must be left (L, N and earthing). Make a bridge at contacts 3 and 4. Take two wires that connect on the boiler plate to + and -. In the Tado thermostat, cancel the wires on the left side (220v) and connect only on the right side to + and -. When setting up Tado you need to set D07 for Ebus. Good luck !!!!
  • gary333
    gary333 ✭✭
    edited February 23 Answer ✓

    I would recommend you top your boiler up a little :) The water pressure is a bit low. The gauge is not the best on the 837/937 compared to the 838/938.


  • Thanks Montage, does it make a difference which side you bridge on then? Like a pro or con? lol

  • Thanks Montage,

    I looped the 230v side, got paranoid if i looped on the 24v side it would fry the board due to having a 230v system lol

  • Thanks BauBau,

    All done and dusted on the weekend 😁


  • Good luck !!!! :) :)
  • Did you manage to solve the problem? . Give a signal when you're done. Good luck with your work.
  • Hey BauBau,

    Yep all done and working fine thanks for the help :)
  • I'm glad you made it. Does modulation work well? Congratulations !!!!
  • It works well, boiler temperature stays relatively low apart from first thing in the morning when the schedules start, the only fault I can find is that certain rooms drop temperature quickly so it causes a heat request to the boiler and so sometimes it's in anti cycling mode (radiator icon flashing) but I guess that's more of a fault with my old house rather than the system itself
  • Welcome to the Vaillant anti cycling Olympics. I’m in first place with that one at the moment lol.
  • I was getting paranoid originally but now I have learnt to accept it :lol:
  • Me too. Luckily I’ve got 5 years left of the warranty, so if it breaks hopefully it’ll be within the period :).

    I’ll replace it with a heat pump electric system if it goes pop after that.