Help me understanding my heating installation and replacement

@Brambles I just want to say I'm amazed at your level of knowledge and memory, I've only known a few as well informed as you.

Brambles said:

Rory,

The units are Heatmisers - albeit they may be badged under a different brand name. My understanding is that Teabag wants to use Nest so he /she is removing the 12v UFH 8 RF unit and the Neo Air stats and replacing it with the 240v UFH 4 unit coupled to Nest. I assume he is doing this because Neo Air which is compatible with the UFH 8 RF don’t include smart TRV’s in their range to control the radiator circuits (you have to use air stats and zone valves) An alternative would be Evohome to control everything - but that is In a different price league.

It is a fairly straightforward change, provided you wire the UFH 4 (240v) correctly and don’t just copy the 12v UFH 8 RF wiring.

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Hi Rory,

It's a pretty good sum up.

I am confused by the 12v vs 240v part though, the wiring diagrams are both showing they are operating 240v actuators?

Thanks

Teabag

The inputs to a Heatmiser UFH8 are 12v through Neostats - in the RF version you dont see it, but the actuators et al are switched at 12v with a 240v output.

For Nest, I assume you are switching at 240v with 240v outputs, hence using the Heatmiser UFH4?

My comment on not copying the UFH8 wiring across to the UFH4, but to work to the wiring diagram and “bell” the existing wires is good practice to avoid mistakes.

From your photos one of the valves is only taking a positive feed from the UFH8 - I assume that it works and that the installer was short of a core to bring neutral back to the UFH8 - that is not good practice. So, if it was me, I would check out all the wiring.

There is nothing wrong with what you are proposing with Nest and with the UFH4 it will work - apologies if I confused you.

Brambles said:

Teabag

The inputs to a Heatmiser UFH8 are 12v through Neostats - in the RF version you dont see it, but the actuators et al are switched at 12v with a 240v output.

For Nest, I assume you are switching at 240v with 240v outputs, hence using the Heatmiser UFH4?

My comment on not copying the UFH8 wiring across to the UFH4, but to work to the wiring diagram and “bell” the existing wires is good practice to avoid mistakes.

From your photos one of the valves is only taking a positive feed from the UFH8 - I assume that it works and that the installer was short of a core to bring neutral back to the UFH8 - that is not good practice. So, if it was me, I would check out all the wiring.

There is nothing wrong with what you are proposing with Nest and with the UFH4 it will work - apologies if I confused you.

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Thanks mate, appreciated your feedback.

I think you are showing that I neglected the difference in tensions between the Next and UFH4 / 8. The UFH4 is expecting 12V to from Neostats and the Nest would send 240v. I was thinking of indeed replacing the Neostats from the UFH4 diagrams by the Nest wires directly. Am I good to send back the UFH4?...

EDIT: the below diagram shows it's actually expecting 240v thermostat, so I should be able to plug the Nest Links directly?

UFH4 is 240v signal - fine for Nest. UFH8 and UFH8 RF (albeit this in hidden in the RF version) is 12v signal.

Brambles said:

UFH4 is 240v signal - fine for Nest. UFH8 and UFH8 RF (albeit this in hidden in the RF version) is 12v signal.

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Okay, we are on the same page, phew.

Thanks again.

Brambles said:

UFH4 is 240v signal - fine for Nest. UFH8 and UFH8 RF (albeit this in hidden in the RF version) is 12v signal.

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So to clarify for my own piece of mind the UFH4 switches 230 from stat to actuators but UFH8 and RF switches 12 to and from stat and to actuators?

SJB060685 said:

So to clarify for my own piece of mind the UFH4 switches 230 from stat to actuators but UFH8 and RF switches 12 to and from stat and to actuators?

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If I got it right all the way the UFH8 is switching at 12V on the board but activate the actuators using 240V. It must have been simpler to use 12V as it's done remotely / internally.

SJB - despite the similarity in names the controls are very different in the way you can integrate them into a control system.

UFH4 is a simple controller that can be easily adapted to utilise different actuators and thermostat inputs for UFH and a zoned radiator group.

UFH8, is direct wired, with a wider control capability. 1 to 7 of the zones can be used for UFH or a radiator zone through software settings at the thermostat. Zone 8 can only be used as a radiator zone. It is designed for use with Neo Stat and is not user friendly to integrate with other manufacturers stats / timers.

UFH8 - RF is as UFH8 but is only suitable for use with Neo Air stats / timers - unless you are a Geek on understanding protocols.

The issue, as I see it, with the Heatmiser range is that they are excellent for UFH - possibly best in class, but when you want to combine a number of radiator zones in conjunction with UFH zones, the user interface becomes overly complex. Their product range / capability for the control of radiator zones is a long way from best in class.

Teabags preference to convert to a single wifi / app enabled system that the user can understand is a common request.

Thanks for explaining that buddy

Hi folks,

I just want to update my own thread after 6 months+. I actually did all the work discussed above back in March and got enough time to conclude everything has been working as expected since I changed my system for a Nest controlled one.

When I did in March it was still a solid winter so it gave me the confidence the heating was still working as good as my previous thermostat with all the convenience of the Nest system.

I am attaching a picture of the final wiring with the three Nests on the UH4. I am sure there is room for improvement, on the actual cable management but also on some wiring themselves (like the HW valve only wired on the L on the UH4). Second picture is how it looks once all boxes are closed.

I didn't put any picture of the wiring for each thermostat but it was reasonably simple. I used an LED transformer for each of them in order to get 12V next to my 220V sockets. Last picture attached is the one of a working thermostat!

Anyhow I hope this can help someone else looking for a similar setup.