Drayton Wiser with heat interface unit

20 Dec 2022
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United Kingdom
I live in a building with communal heating provided via a heat interface unit in the flat. There is no boiler in the flat. Heating is controlled via a battery-operated wired thermostat located in a very inconvenient place. From what I can see all my current thermostat does is turning the heating on or off (only two electrical cables connected to it). It is essentially a switch.

I want to replace it with a smart not-internet connected system, like the Drayton Wiser, where I'd have a wireless thermostat that I can place in a more sensible place and control it via an app.

What I can't figure out (and I tried asking the Drayton people but their sales staff are clueless) is whether the Wiser Hub is compatible with this system. The Wiser installation manual does not mention a scenario where there is no boiler.

Could you please tell me how I would install the Wiser Hub here, and if that is not possible, what other alternatives are there that would work?


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A Wiser single zone (i.e. combi) would support your requirement with the caveat that you need to provide a 240V supply to power the Hub itself. The existing pair of wires you have on your current thermostat would handle the temperature related switching. However it's highly unlikely you will have a suitable mains supply behind the current thermostat.

Otherwise a battery powered option such as Nest E is your best choice. Nest E does have the advantage that it's hub is battery powered and therefore avoids the need to locate a mains supply.
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Thank you both. Based on what you said I identified the wiring diagram in the installation manual and attached it below. It will need four connections:
1. N (2) - neutral - currently missing, would need to be provided
2. L (1) - live - currently missing, would need to be provided
3. COM (4) - the brown existing wire
4. ON (5) - the black existing wire

Is the above correct? I think I'll call an electrician to wire it up but want to make sure I understand and can explain to him what needs to be done.


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Unless you already have power behind the current thermostat I'd probably say you should take an alternate route.

If power is available you would have five connections Live, Neutral & Earth plus the switching pair. Whilst the Hub itself is double insulated the back plate has a connection for a earth wire. The connections on the Wiser back plate used are N, L , E, 1 & 3. The numbers you mention relate to a wiring centre which you don't have. Your brown & black would go to 1 & 3 on the Wiser back plate.

You should investigate if Nest E meets your requirements.
Thanks. Behind the thermostat wall there is a utility space with the consumer unit. I was thinking that in the worst case I could have an electrician add a new circuit for this purpose. Do you not think this is a good idea?

Regarding the Google Nest E, with Google's reputation for shutting down products when they are not profitable enough, I have no confidence in it being available and supported in the long term. I also understand that it does not work fully without an internet connection and Google's servers being available. The Wiser works with no internet connection and does not rely on the vendor keeping servers active.
There is also a light switch right next to the thermostat - if using an existing light electric circuit for this is acceptable, there is live, neutral and ground available about 15cm away.
I am no electrician and would defer to someone more qualified to say if it's a good idea or not. If power can be provided safely in manner that does not compromise anything it is doable.
You actually have a grey wire which could very well be a neutral wire safely terminated, and the live in (brown) could very well be a permanent live, easy enough to test/trace.
OK, let me investigate the wires with a multimeter. Looking at the photos, looks like there is a green-yellow wire too so possibly there may be everything needed there already.
So here are the results:

HIU circuit breaker OFF
- yellow-green to brown 21V
- yellow-green to grey 0.5V
- brown to grey 11V

HIU circuit breaker ON
- yellow-green to brown 234V
- yellow-green to grey 12.5V
- brown to grey 158V
It could still be a neutral wire, but just not connected the other end?
I found a junction box above the HIU. There is a grey wire with a blue sleeve wired to neutral.


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In the junction box at the terminal block I measured the following:

HIU circuit breaker OFF
- yellow-green to brown 0.4V
- yellow-green to grey 0.4V
- brown to grey 0.02V

HIU circuit breaker ON
- yellow-green to brown 233V
- yellow-green to grey 0.4V
- brown to grey 232V
In the junction box at the terminal block I measured the following:

HIU circuit breaker OFF
- yellow-green to brown 0.4V
- yellow-green to grey 0.4V
- brown to grey 0.02V

HIU circuit breaker ON
- yellow-green to brown 233V
- yellow-green to grey 0.4V
- brown to grey 232V
That’s more like it, don’t know why you weren’t getting those results before. Providing it’s a permanent neutral, then you shouldn’t have issues with the wiser.

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