Honeywell CM707 To Hive wiring issues

Joined
7 Dec 2019
Messages
5
Reaction score
0
Country
United Kingdom
Hi all, I am a year one apprentice who is looking to change the Honeywell CM707 thermostat for hive.

Below are the pictures of the current wiring. I have connected a voltage tester between Line and Neutral at the thermostat and it read 50V. The property has old wiring and everything is protected with cartridge fuses with no labels.

My understanding is the Hive needs a 230V supply?

Any help would be appreciated, a bit out of my depth but would be ideal to get a good understanding not just to get it working but to learn

Thanks
 

Attachments

  • D2A242C0-94EC-4340-B895-B40FF9150800.jpeg
    D2A242C0-94EC-4340-B895-B40FF9150800.jpeg
    168.3 KB · Views: 1,893
  • 109F7F40-5744-4D2E-BCCB-BFEDD399131D.jpeg
    109F7F40-5744-4D2E-BCCB-BFEDD399131D.jpeg
    162.4 KB · Views: 920
Sponsored Links
The hive receiver base is (should be) installed at the boiler or wiring centre where the supply will be available.

The thermostat and its wiring then become redundant.
 
Nest e would work from that point, but not Hive, as @EFLImpudence says one would normally fit the wireless thermostat base at the boiler, wiring centre, or programmer position, with only the sensor at the original thermostat location.

You say old property so possibly not a combi boiler, with old or oil boilers they often switch off/on, with modern gas boilers they adjust output up/down, old and oil had all the storage of hot water out side the boiler, and also pumps and valves outside the boiler, because Hive has the common internally liked to the line in the duel channel version, it can't be used with many systems. Both due to voltage and with very old systems you need the supply to N/C and N/O with the com going to boiler.

To convert this C Plan C-Plan_old2.jpg to work with a smart thermostat needs something like this C-Plan_basic_Nest.jpg but Hive can't be wired that way, to be frank it may work in theory, but in practice in many houses the water will thermo syphon through the pump when stopped, so it would be better to convert the pipe work where one can, I say where one can as old boilers often don't have a run on, so rely on the cylinder having no valve to stop over heating, and so only way to fit valves is the Y Plan as the default is DHW so again some where for the heat to naturally go.

So many houses today have combi boilers with some method of modulation for the output (being able to reduce output) we tend to forget there are still some old systems around.
 
Sponsored Links
The Honeywell CM707 terminals A & B are simply connected to an internal on /off switch. When the stat turns the heating 'on' the wires in A and B are connected together, when it's 'off' they are not. Various voltages can be used and will come from the boiler directly, but as far as you are concerned the two wires are just connected to a simple on / off switch.

The corresponding terminals on the Hive Single Channel version are (1) 'Common', and (3) 'Heating On'. The voltage doesn't matter because the Hive Single Channel receiver has a voltage free switch, the same as the Honeywell does, so will switch whatever voltage is applied from the boiler.

However, in addition, and as you figured, the old thermostat is battery powered but the Hive receiver requires a permanent 230V supply to power it connected to N & L. This should come via the same FCU supplying the boiler.

You don't give any details of the system the thermostat is connected to, but exchanging the Honeywell CM707 for the Hive would be suitable for a combi boiler that generates hot water instantly when a hot tap is opened and does not have a hot water cylinder connected to it that needs controlling. Systems with a hot water cylinder connected use the Dual Channel Version of Hive, and the wiring is completely different, primarily because there aren't any wires that control the hot water at the room thermostat, and it doesn't have voltage free switches, one side is connected to the live terminal internally.
 
However, in addition, and as you figured, the old thermostat is battery powered but the Hive receiver requires a permanent 230V supply to power it connected to N & L. This should come via the same FCU supplying the boiler.
I am not convinced that with a mains powered thermostat the supply needs to come from same point as boiler when fitted with volt free contacts. The whole idea of volt free is there is no connection between boiler supply and thermostat supply.

My house has 10 independent supplies to central heating, one from a FCU (fused connection unit) in the granny flat under house, and nine from pairs of AA batteries one pair in each TRV head.

There are rules when supplied from more than one source of energy. Like "A main switch shall be provided for each source of supply and a durable warning notice shall be permanently fixed in such a position that any person seeking to operate any of these main switches will be warned of the need to operate all such Switches to achieve isolation of the installation. Alternatively. a suitable interlock system shall be provided."

So there could be a case where a sticker is required saying some thing like this unit stays live when boiler is switched off, but there is nothing on battery powered units, so why should there be anything on mains powered?
 
I am not convinced that with a mains powered thermostat the supply needs to come from same point as boiler when fitted with volt free contacts. The whole idea of volt free is there is no connection between boiler supply and thermostat supply.

It's good practice for safety. When the FCU is turned off it isolates the whole heating system and all associated components. Someone working on the heating system for example may not realise that a receiver is supplied from elsewhere and receive a shock after turning the heating system FCU off. Manufacturers often include it in their installation manuals.

e.g. from Vaillant
instructions-jpg.157752



Nest say the the Heat link should be fed from the "boiler terminals or wiring centre" which are of course connected to the FCU, and Hive refer to the receiver being powered by the same supply as the "central heating system". Of course the instructions cover both 230V and 24v installations so you could argue that the one instruction fits all, 230V being the 'worst case'.

From an operational point of view of course, you are quite right, there is isolation of the switching voltage and operational voltage by the volt free contacts.
 
Last edited:
There is no provision to power my TRV heads from the same supply as the boiler, nor is there an option for hard wires LAN, it has to be battery powered and has to use wifi or blue tooth. So I have 10 separate supplies to my central heating.

I have in other house a battery powered wall thermostat, so again two separate supplies. Be it 3 volt, 12 volt, 24 volt 48 volt or 230 volt the supplies are not linked.

Running 5 core cable from the boiler to the thermostat with 24 volt on two cores and 230 volt on the other two cores with the latter being AC is not really what should be done as the capacitive and inductive linking in the cable could result in over 50 volt above earth being present in the extra low voltage cables, you would need to run them as separate cables with either steel between or some distance.

OK I know we all do use 5 core, but that does not make it right. I will also agree where possible I would use one FCU to supply all central heating, this house had three FCU on the central heating plus a 13A plug, and I rewired so now they all come from same FCU, where before not even from same consumer unit. But I have worked with many machines with duel or more power supplies, in fact my central heating in all houses had at least two, being supplied with both gas and electric, or oil and electric. Does not matter if air, gas, oil or electric they are all power supplies.

So it was common to fit a valve so if the electric was cut, so was the air or gas, however even this needed so thought, having an emergency stop kill the air supply can result in something dropping, so often twin air supplies, one which is not cut when e-stop is pressed. This is a safety feature decided on after doing a risk assessment.

So in this house, if the supply to the front of house ring is lost, I can't turn off my Christmas lights at the back of the house, as the socket powering the lights is wifi controlled and router is from front of house sockets, so no router, no control. Same applies to lights, or any other wifi controlled system. So even my TV has multi supplies, as to work it needs router, main sky Q box, satellite sky Q and TV all to be powered, and of course a satellite signal.

With a volt free thermostat the 230 volt power is nothing more than a battery eliminator. I do see the problem where some one replaces a volt free with an non volt free, but we can't really stop some one doing this, all we can do is put a warning sticker as some one working on the thermostat may prove dead but a timed supply could then make it live again.

BS7671.2008 said:
537.1.5 Where an installation is supplied from more than one source of energy, one of which requires a means of earthing independent of the means of earthing of other sources and it is necessary to ensure that not more than one means of earthing is applied at any time, a switch may be inserted in the connection between the neutral point and the means of earthing, provided that the switch is a linked switch arranged to disconnect and connect the earthing conductor for the appropriate source, at substantially the same time as the related live conductors.

Note if from same earthed system this does not apply. Maybe changed with BS7671:2018? but it may be bad practice, but can't find a rule to stop using two FCU from the same supply, and not many houses have two independent supplies.
 
Hi guys I have a little bit more info

The boiler itself is a Worcester Greenstar 30Si

There is no supply that I can see currently for the Hive receiver.

Any help appreciated

Thanks for input so far
 

Attachments

  • 7A010D0D-88F5-444F-939D-87849C0AD3E5.jpeg
    7A010D0D-88F5-444F-939D-87849C0AD3E5.jpeg
    188 KB · Views: 306
This is the 230V supply for external controls

1.JPG


Remove all of the existing wiring to the existing external controls, but not the white link to the tap symbol, then, for a single channel version of Hive:

Hive N goes to Boiler '230V OUT N' [(9) in the diagram above]

Hive L goes to Boiler '230V OUT L' [(9) in the diagram above]

Hive 3 goes to Boiler 'LR' [with the radiator symbol (8) in the diagram above]

Add a link between Hive terminals L and 1.

On another matter, this is the incoming mains supply, I would only expect to see one cable in here. Where does the second one go?

Capture.JPG
 
Last edited:
OK thanks. That redundant cable should go then, and you want to end up with this.

Hive.jpg


The above is for a single channel Hive. If you have the dual channel version of the Hive, the wiring terminals are different but you can include time control for the hot water, should you want to add this, as per the below.

Hive 2.jpg


As combi's provide instantaneous hot water when a tap is opened, most folks don't bother adding the hot water control, but it would stop any hot water pre-heat function working when set to off.
 
Last edited:
Great, I’ll look to get this installed today. Thank you so much for all your input guys

yes we have the single channel
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top