Wiring for "suspected" y plan and tado extension kit installation

[Paludatus]

I am attempting to replace my Central heating and hot water programmer (Honeywell st6400c) with the tado extension kit, I already have a tado smart thermostat installed on a hard wired room thermostat.
When looking at the junction box wiring beneath the programmer it didn't seem to match any wiring diagram I can find. Unfortunately the previous home owners did a lot of home improvement, including moving the boiler with the mid position valve (I think) in the loft covered, so I can't trace all the wires.
I have included photos of the junction box and a written form of all the connections. I have a few wires that I'm unsure of what they connect to, I realise they must be the mid way valve, cylinder and boiler, but can't figure out which is which.
My question is, do I try to re wire them and then wire in the new tado extension kit, or just replace the old programmer with the extension kit leaving the junction box as it is hoping that the current wiring is just about correct (given it was working before).
Apologies for the long past but struggled to explain the issue, thank you in advance for any help.

 

[stem]

The Honeywell will have a wiring diagram printed on it something like this:

The Tado extension kit is wired as below: [Jumper position 2 is selected for Y-Plan]

So as you can see, the wiring connections are the same. Lucky you! So, the existing wires in the Honeywell simply go to the Tado terminals that have exactly the same function. [The green / yellow wire in terminal 1 is being used as a live wire, so it should at least have a brown sleeve over it to identify this]

I believe that your existing Tado wired thermostat will have the connections as shown below, with wires connected to NO and COM. If yours is different post back the details.

Trace the thermostat cable back to its origin which according to your photograph of the wiring centre you have done already. Note where the wires from the cable are connected to the wiring centre and disconnect the cable completely. Then insert a link between the two terminals that previously contained the thermostat wires that were connected to the thermostat NO and COM terminals, so that they are electrically connected.

As an alternative to the above modification to the wiring centre, and provided that the existing room thermostat is suitable to be used wirelessly with the new extension kit and you want to retain it. You could put the two wires presently in NO and COM together in an unused 'parking terminal' so that they are connected together at the thermostat end instead. Electrically it achieves the same thing as making the link at the wiring centre end.

 

[Paludatus]

Thank you very much for your reply, I've only just been able to get round to having a look at it again.
I initially installed it as you suggested but the heating would not come on, got water did work.
I re wired the thermostat in (as tado suggested, so as wired room thermostat) and still same problem.

I have managed to trace back wires from the junction box, only error I can potentially see is that the midway valve (grey and orange) may be the wrong way round as both are black wires from previous owners wiring, could that make a difference?

 

[stem]

Yes, it would matter if they were the wrong way around. On a 3-Port valve, the grey wire is connected to hot water off from the programme and cylinder thermostat, and the orange is the switched live to switch the boiler on when heating is required. They have totally different functions.

Assuming that you haven't moved them, and it was working correctly before, then they will be correct.

All you should have done is swap a Honeywell with two on/off switches for a Tado with two identical switches. Electrically nothing should have changed.

Joining the two wires at the thermostat together is replicating what the thermostat would have done when it was calling for heat. So even if the thermostat wasn't even there but the wire from COM and NO were connected together the heating should have come on.

Have you checked that all of the wires are well connected and the terminations are tight?

If the wiring is correct. As you have added a new extension kit to an existing thermostat are they paired?

 

[Paludatus]

Thank you again for your help.
The programmer was working fine prior to any change (before installing thermostat), since then the central heating does not always turn off again, despite the app stating it is not calling for heat. After discussion with tado they suggested that one solution would be the extension kit, hence the purchase and install.
I have left all electrical connections as they were, after checking their integrity. I have paired it with the internet bridge and tado confirmed it was working from their end but still no central heating. It will turn on boiler for hot water but does not fire for call for heat.

I have had to reinstall the old st6400c as we needed heating in the house. Not sure what my next steps would be. I've messaged tado support as well but they have long wait times at present, so each time I have to replace the st6400c to get heating back whilst awaiting a reply from them.

As you said the electrical connections are likely correct given it was working before. Whilst tracing wires in the loft, there are 2 from the boiler, one (3 core unk.inf from diagram) just goes through a fused switch and is a mains connection, the other is only wired only to earth and then with orange from midway valve and I think to the cylinder, the neutral wire is cut and not connected to anything?

Beyond electrics I'm left with software (which hopefully tado will be able to help with) or another component in the heating setup but again unlikely as it was working before.

Any other suggestions? Thank you again for your help

 

[stem]

If you have swapped the Tado extension kit back for the old thermostat and it is working OK, then the wiring is correct. As I said before the ST6400 has an 'on' and 'off' switch for the heating and, an 'on' and 'off' switch for the hot water. The Tado extension kit has exactly the same.

If the thermostat is communicating with the Tado extension Kit OK, then all I can think of is that you may have faulty Tado.