Replacing Honeywell ST9400C with Hive Hot Water and Heating

[lukeyb123]

Hi,

I am looking for some advice regarding replacing my Honeywell ST9400C with a hive hot water and heating system.

I looked online, it seemed simple enough, ordered myself a hive but today I looked a bit closer at the wiring and I'm a little confused as there are more wires than I anticipated.

I also have a thermostat wired into the wall which is probably confusing things further.

I have attached a few photos of the wiring I have found.

Stumbled across this forum and seemed like a good place to ask the question.

Any help would be much appreciated.

 

[RandomGrinch]

Yes, the extra wires to the thermostat would add to the complexity.
What you do next, depends on what you wish to achieve.

If you would like the least complex install, simply replicate all the connections on the ST9400C onto the Hive receiver backplate.
Then turn your existing thermostat up to maximum.

If you would like to decommission the old stat and remove the wiring, it appears as if you have a 3 core (+earth) cable with a red, blue and yellow core.
I believe the Red core from that cable comes from terminal 4 on the ST9400C, the Blue core comes from the N terminal on the ST9400C and the yellow core comes back to a separate terminal block behind the backplate.
I wonder if you can confirm that?

 

[lukeyb123]

Hi, thanks for the quick reply.

In all honesty, I plan to change the boiler to a combi or potentially a heat pump in the near future so the first option might be the best suggestion.

In relation to the wires for the second option, is there any other way to confirm this other than using a wire tracer?

Cheers

 

[RandomGrinch]

In relation to the wires for the second option, is there any other way to confirm this other than using a wire tracer?

Partially, what I was suggesting was to have a look carefully behind the backplate (with the power safely isolated), to see if the coloured wires I've listed above, do indeed come from the same cable.
If they do, there is a high likelihood that it is the cable to the stat.

 

[lukeyb123]

There is a white cable right at the back (photo attached) this has 4 wires coming out of it - red, blue, yellow (which is what is on the thermostat) and also an earth.

There is a cable coming from the boiler with 5 wires.

Then there are a further 2 cables coming from the back box - they both have red and black wires. One of them has an earth too.

Any ideas?

 

[RandomGrinch]

There is a white cable right at the back (photo attached) this has 4 wires coming out of it - red, blue, yellow (which is what is on the thermostat) and also an earth.

Yes, and does..

the Red core from that cable comes from terminal 4 on the ST9400C, the Blue core comes from the N terminal on the ST9400C and the yellow core comes back to a separate terminal block behind the backplate.

?

 

[lukeyb123]

Hi,

Sorry for the late reply but it looks like the cable coming from the thermostat has 4 wires coming out of it - red, blue, yellow (which is what is on the thermostat) and also an earth.

The earth goes into a junction box at the rear of the ST9400C.

The red goes into position 4.

The yellow goes into position 3.

The blue has a black covering over it but goes into N.

Does that make sense?

 

[RandomGrinch]

The red goes into position 4.

The yellow goes into position 3.

Thanks,
That's what I was afraid of.
The yellow wire being in terminal 3 (HW on), means that the white cable isn't directly connected to the thermostat.
Instead, it may be connected into a separate wiring centre, or junction box.
If you wish to remove the stat, some further investigation is required, to find where the cable goes.
Sorry it wasn't quite so straightforward.

 

[lukeyb123]

No probs, thanks for your help, it is much appreciated.

Would the first option you mentioned still work?