Buderus Logamax U154-20K wiring


I have this my bathroom - it has a mains power going into it, but there are no plug sockets to power the TADO in addition to the boiler.

My questions will seem likely childish or simplistic but Im not an engineer and the TADO installation app for this model doesn't make a great deal of sense unless they mean simply to turn the whole boiler on an off each time rather than the water pump and the flame.

The main board looks like this inside - N and L are from the live outside - over on the right the black cable appears to be what I could likely activate the gas and pump without switching on and off the whole boiler. If so :

1) Can I power the TADO by feeing the N and L into the TADO and THEN froth TADO into the boiler? eg by using the relay connections on the TADO? (there is no plug socket in my bathroom where the boiler is.) or do I some how connect the TADO directly onto the terminal block?

2) Furthermore inorder to start stop the heating and pump how is the TADO connected to the white terminal pair that feed to the black cable? What confuses me most is that the app has told me to connect somewhere (not not exactly clear) on the terminal block to the analogue points of the TADO. This doesn't make sense really.

(I believe these are also made by Worcester Bosch - does anyone have access to an English manual for full installation - I am not sure whether to use the relay or the analogue points on the TADO (ps not an engineer) but can't find a full manual in any language.)

Many thanks.

Best Answers

  • Montage
    Answer ✓

    I can’t see anything below, but it sounds like you are heading the right way.

    Relay can only issue a demand for heat. Digital can tell it how big a flame to fire. This is for CH only and will usually ignore the dial on the boiler (or it wouldn’t work properly).

  • Montage
    Answer ✓

    Just to add, early in the thread we didn’t really have data show the boiler supported digital, and so we focussed on relay being the only option. No other reason.

  • Montage
    Answer ✓

    Yes. I wouldn’t like to speak for all digital varieties, but probably nothing over 30-40 Volts.

  • johnnyp78
    johnnyp78 ✭✭✭
    Answer ✓
    Digital is low voltage. @Montage i think analogue is something else - something closer to varying potential than switched live. Either way I think it’s rarely used.


  • I should also point out that there is a grey vertical block to the right of the green circuit board that may also be useful - there's some Russian videos where wiring in has been done to this of weekly planners etc.

  • What could possibly go wrong.

    You could either power the Tado from the sources the boiler power, or piggyback the the L and R coming in. Don’t run this via the Tado relay connections.

    You mention relay and analogue, but probably mean relay and digital. You want relay and need the LS and LR (currently bridged). This is a mains voltage and needs to use the relay connection. LS is the switched live and LR is the one that Returns the live when Tado energises the relay.

    The currently bridged connections mean the boiler is in the state of demanded heat all the time.

    Hope that helps.

  • that’s really helpful-what’s really worries me however is the digital says only max 35
    volts which is der less than the LS abd LR- also will theis literally just turn the burner and pump on and off or will it modulate the temp of the boiler (which has a separate manual temp setting ahyway)?
  • sorry i forgot to mention that the tado instructions on the app for my boiler says plug the wires from the boiler into the analogue/digital sockets on the TADO but there’s nothing less than 35 volts coming out of the boiler hence the confusion
  • eg i thilk the tado instructions are wrong!
  • johnnyp78
    If you run a live current into the digital terminals on Tado you’ll blow the pcb so I wouldn’t do that. Are you trying to install it digitally or relay?
  • literally wondering which wire goes where so that when the tado wall or radiator sensors say it’s warm enough the boiler will stop burning gas and pumping water
  • johnnyp78
    I’m baffled. Do you know whether you want to install it via relay or digital? If digital, does your boiler support digital connections?
  • sadly not as there’s no manuals for my boiler-it has two manual dials to set water and heating water temp plus a digital readout that tells you the water temp but that’s it-however Tado have an(useless) installation page saying it’s compatible
  • johnnyp78
    There’s no reason why it wouldn’t be compatible with a relay installation. Follow what @Montage said. You haven’t said what Tado device you’re trying to install but assuming it’s a wireless receiver, follow the instructions for combi boiler, switched live in section 4.

    I don’t know much about the analogue connections but they’re very rarely used in the uk. If the Tado app is telling you to use them I would check with Tado support where you’re supposed to connect.

  • Your digital and low voltage connections appear to be in the top right of your last two photos. They have a bunch of wires across them, but I can see 24V mentioned.

  • i did wonder about the orange thing too which also has a bridge across it- if my boiler has manual dials for heating and hot water i presume TADO won’t override those i just set them for best temp and then decide whether to use relay or digital? I get conflicting information what relay or digital does or whether i can even use them?
  • hipponax1973
    edited January 2023
    ok i’ve got the schematics translated and it’s the wiring on the right called st19 tado says i should put into. See below
  • So before I go on can I thank everyone for their help:)

    1) In the top right of this first picture (starts para 5.2.3) you will see the ST19 - this is the bridge tado has asked me to look for (see below) which is then fed back into the analogue. From what Montage says that is probably 24V - what's interesting is almost everyone has said use the Relay switches but am I right in thinking that the TADO is essentially an EMS Bus or RC controller? and therefore why it want me to put into the digital?

    2) Apart from the voltage what's the main difference between the relay and the digital - is the latter more definable eg temp etc and the relay simply an on off from the mains? Maybe im asking the wrong question

    3) with regards powering the TADO as no plug sockets in the bathroom, do I put it in between the mains and the boiler, and then have wires off the live on the TADO feeding power to the boiler, or piggy back the power off the Live on the left hand bridge in the boiler and leave the mains where they are ? cheers.

  • Montage thanks for the info re above the flame I think that probably confirms that I should be feeding off the ST19 back to the digital :)

  • Yes, it’s the preferred method for better efficiency (where the boiler supports it).

  • Glad we got there in the end.

    Your boiler clearly accepts all 3 types of switching. It does the mains level switched live, digital and also low voltage switched (which is called analogue here).

  • aha- digital is low voltage too yes?
  • excellent now to see where to put the temp sensor best - are there good links for principles? - Ive posted another Q with layout of flat