Replacing a Honeywell ML1 5SB, UK with a Hive Mini (Single channel)

[danMozzer]

Hi,

I'm looking to replace my current Honeywell thermostat with a Hive Mini, looking at the original wiring and then the wiring guide for the Hive Mini, I'm a bit lost.

For reference, when the thermostat is turned up high, it clicks, and the combi boiler fires up and turns the heating on. (I know I just explained how a thermostat works, but I wasn't sure if this changes the way you would wire the Hive Mini)

Note: I should also mention that there is a mechanical timer module built into the boiler, but it's not used and is bypassed by having it switched to 'Fixed on' so that only the thermostat controls when the heating is on basically.

From the wiring below, I can tell that the Neutral is going to '2', and the Live is going to '1', (and of course, Earth is going to Earth) but I'm not sure about the Black wire going to '3'.

Below is an image of the wiring diagram on the cover, which I think is what is throwing me off.

I have gathered (looking at the wiring guide for the Hive shown below) that Neutral will go to 'N', and Live will go to 'L', but my question is, where would the black wire go, and can I replace the Honeywell with a Hive mini?

 

[CBW]

3 is switched live.

Honeywell to Hive:

L (1) to L
N (2) to N
Call for heat (3) to heating on (NO)
Place a link wire from L to Common

 

[RandomGrinch]

I know I just explained how a thermostat works, but I wasn't sure if this changes the way you would wire the Hive Mini

It doesn't!

there is a mechanical timer module built into the boiler, but it's not used and is bypassed

Good!

I have gathered (looking at the wiring guide for the Hive shown below) that Neutral will go to 'N', and Live will go to 'L',

Yes.
Plus green/yellow to the earth terminal.

where would the black wire go

To Hive terminal 3 (NO).
You also need to add a small link wire between L and terminal 1 (COM)

can I replace the Honeywell with a Hive mini?

Yes!


...shucks, beaten to it by seconds!

 

[danMozzer]

Thank you both (@CBW & @RandomGrinch), I really appreciate the help and responses

 

[danMozzer]

Hi,

Sorry to revive my post, but I've only just had a chance to recently buy the Hive Mini and attempt a replace, and unfortunately, it seems there is a problem, I don't think the wiring we all thought is correct, and I'll explain why.

First, I followed the wiring that both CBW and RandomGrinch provided (thank you again), however, when turning the power back on, I noticed nothing was happening, the Hive Receiver was off, no sign of life at all, which worried me for a moment, so I thought I would connect the previous Honeywell back again just to make sure something hadn't gone wrong, and sure enough it was fine.

Then I decided to check with a multimeter as I was wondering why the old thermostat worked, but the Hive didn't, and well, my findings are... interesting...

(I would have attached images, but taking a picture while holding a multimeter wouldn't work so I'll just describe what I did)

First, I connected the black probe to the Earth (Ground), and then I went one by one on each of the other wires with the red probe and found something interesting.

(I'm reattaching the image of the wiring so you don't have to keep scrolling up)

The 'Grey' wire ('2') (that has a bit of blue sleeving on it) displayed a voltage of 142 volts, that seems strange to me, but maybe that's right to everyone else.

The 'Black' wire ('3'), which does have a bit of brown sleeving on it, read... 243 volts? This was the wire we thought was the 'NO' for the Hive to control the heating.

However, the brown wire (going into '1') read... 0 volts... so I'm not sure what has happened here and if maybe whoever originally wired this somehow made everything confusing/complicated, but could it be that this thermostat was either wired incorrectly, or it's just that the there was a misunderstanding, because I'm assuming this is why I couldn't get the Hive to turn on?

Any advice on this would be a great help.

 

[RandomGrinch]

The 'Black' wire ('3'), which does have a bit of brown sleeving on it, read... 243 volts? This was the wire we thought was the 'NO' for the Hive to control the heating.

Ok, then try a swap - connect the black (oversleeved brown) wire to L and the brown wire to 3. It didn't really matter which way around the connections were in your old stat.

The 'Grey' wire ('2') (that has a bit of blue sleeving on it) displayed a voltage of 142 volts, that seems strange to me, but maybe that's right to everyone else.

If measured correctly, this voltage is unexpected. It may suggest that your grey (oversleeved blue) wire, isn't actually connected to a neutral, or there is a fault elsewhere.
If you try swapping the wires, as above and the Hive still doesn't operate, we may need to trace the cable back to its original connection.

 

[danMozzer]

Thank you, unfortunately, the hive still hasn't fired up, but as electrical work is only something that I have a basic (dare I say) competent understanding of, I've decided that I'll just have an electrician take a deeper look, as they will more than likely need to check the boiler too.

I did double-check the voltages again with the multimeter (while the wires were connected to the receiver), and the 240v was hitting the Live, and interestingly, the neutral returned to 0v, so I'm not really sure why it still didn't fire up.

I had a spare plug with the 3 bare wires lying around (obviously not plugged in, ) and I decided to wire it up to make sure the receiver is indeed working, and sure enough, it lit up, so something is clearly up with the wiring to the boiler, and I'm definitely not going anywhere near that, which again, is why I'll get an electrician to take look.

For now, I've put the Honeywell back in place. (as I would still like heating of course, it's freezing! )

Thank you again though for your prompt replies, and I appreciate your answers , but sometimes, as I'm sure you'll agree, things are best left to the professionals.

 

[RandomGrinch]

did double-check the voltages again with the multimeter (while the wires were connected to the receiver), and the 240v was hitting the Live, and interestingly, the neutral returned to 0v, so I'm not really sure why it still didn't fire up.

Sorry it hasn't been straightforward.

With the Hive receiver in place the N connection will read 0V.
With the old stat, there was an 'accelerator' resistor, internal to the stat. When you measured the voltage to N on it, you were measuring the voltage drop across this resistor.
Both of these measurements confirm (to me at least!) that the grey wire isnt connected to a neutral - it is just floating at whatever voltage we put into it; and hence why it still didn't power the Hive.
Bad show from the electrician, for oversleeving it blue!

it lit up, so something is clearly up with the wiring to the boiler, and I'm definitely not going anywhere near that, which again, is why I'll get an electrician to take look.

Good for you, for trying
But if you do feel like a quick look at the cable, it really wouldn't be a big job to try and connect the grey to a neutral.

Anyway, good luck and stay warm!

 

[danMozzer]

With the old stat, there was an 'accelerator' resistor, internal to the stat. When you measured the voltage to N on it, you were measuring the voltage drop across this resistor.

it is just floating at whatever voltage we put into it; and hence why it still didn't power the Hive

Ah, I see that's really interesting, it also makes me feel assured that I wasn't wiring something wrong and I'm at least glad to confirm that the Hive wasn't broken.

Good for you, for trying

I appreciate that, that's the one thing I am happy about, is that at least I gave it a go.

Thank you so much again, I really appreciate the info.