Changing Horstmann 425 Diadem To Hive Dual Channel

[Austin Orr]

I have recently bought a Hive dual channel thermostat system to replace my Horstmann 425 Diadem programmer.

I have an oil heating system, hence taking a look at it myself as there is no installation available from Hive.

I am looking for some advice regards changing the backplate and the wiring involved.

IMG_20171108_103518_HDR

• Austin Orr
• 8 Nov 2017

Wiring in plate behind Horstmann 425 Diadem

You can see how the wiring is set up in the current plate. Of course the Hive uses a different plate with less pins.

My questions are do the bridged live wires still have to used in some form with the new plate or i can discard them?

Also, the second lead, where does the live and neutral have to go?

I'm interested to know how this system works at the moment.

Thanks in advance for any help.

 

[stem]

It is basically a matter of identifying what each wire at the Horstmann Diadem does. The diagram below will identify the terminals for you

The Earth Neutral and Live wires are straight forward and will go to the corresponding terminals at the Hive receiver.

The other wires you are interested in are terminal (1) 'Hot water on' and terminal (4) 'Central Heating on' [CH is mislabelled CW in the drawing above btw]

You can disregard the links, the Hive Dual Channel version has these made internally. Remove them and discard them.

Then these wires simply go to the terminals at the Hive that have the same function.

So you will be using:

Earth = Earth
N = Neutral
L = Live
3 = Hot Water on
4 = Central heating on

If you don't have an existing room thermostat then that's it job done.

If you have an existing room thermostat somewhere, then that should be decommissioned properly, you can't just disconnect it otherwise the heating wiring will be open circuit and the heating won't work. If you do have an existing room thermostat, post back details for further assistance.

 

[colinshotts]

That’s very helpful as I am looking at replacing my good old 425 Tiara for a modern Hive system.
I DO have a room stat so further advice on this would be appreciated.
(I have a Worcester Bosch Greenstar 30CDi Conventional, pumped CH with room stat and gravity HW with cyldr stat. My room stat has 3 wires going in to it.)
Thanks in advance.

 

[stem]

Hi colinshotts and welcome to the forum. For future reference, it's best to start your own thread rather than tag your question on to someone else's. It's called 'hijacking' and is against the forum rules. In addition a new post would appear in the unanswered threads section and will more likely to be seen by those that can help, rather than being buried away at the end of someone else's thread. Don't do it now you have started this one though, otherwise you will end up with two confusing threads running on the same subject.

Anyway lecture over and back to your question. To help, I will need to know the make and model of your room thermostat, and what terminal each of the three wires goes to. Unfortunately there are lots of thermostats with different wiring configurations and the colours of the wires used would have been at the discretion of the initial installer.

 

[colinshotts]

My apologies for the hijack, I wasn’t aware of that, I stand corrected and apologies to Austin.
Thanks for allowing me to continue, here are pics of my room stat, (the yellow goes live when there’s a call for heat) I’d appreciate guidance on this.

Also, see the photo (4th) of the backplate wiring of my 425 Tiara, you’ll see I have no wire in terminal 6 (CH Off) everything works fine and has done for years but could this pose a problem when installing a Hive?
Regards

 

[stem]

Good info once again.

The wiring at the Tiara will be pretty much as I described earlier to Austin, with one additional connection, because your system has a 3 port motorised valve. This type of system doesn't need a 'Central Heating off' connection and I would have been worried if there was one!

The Lives and Neutrals are a straightforward swap like for like
The Brown wire in Tiara terminal (1) 'Hot water on' goes to Hive terminal (3) 'Hot water on'
The Black wire in Tiara terminal (3) 'Hot water off' goes to Hive terminal (1) 'Hot water off'
The Grey wire in Tiara terminal (4) 'Central Heating on' goes to Hive terminal (4) 'Central Heating on'

You can disregard the links, the Hive has these made internally. Remove them and discard them.

For the existing thermostat wiring, you have three choices as follows:

1 Remove the thermostat and put the cable in a junction box:
Connect the Live (Red) and Switched Live (Yellow) wires together
Isolate the Blue neutral wire separately

2. If you can trace the cable from the thermostat to its other end, you may be able to remove the cable completely and insert a wire link between the terminals that the Red and Yellow wires originated from.

3. Alternatively, simply leave the thermostat as it is, and move the yellow wire from terminal 3 and put it in terminal 1 with the red.

And whilst you are at it, put some earth sleeving on those bare earth wires.

 

[colinshotts]

Thanks loads, that’s confirmed what I thought, oh and I’ll get some earth sleeving done right away.