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 Thermostat selection with interesting constraints

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simraba Posted - 11/06/2019 : 07:25:01 AM
Hi Guys!
I am looking to buy a smart thermostat but I would like to combine few features that are not present on the mainstream ones (Nest, Ecobee, Tado, etc..).

Feature 1: power supply.
The wall terminal of my place only has two wires with 220v of tension. The current thermostat just closes the circuit to start the boiler. Most of the thermostat require batteries but I would like one that is able to use the 220v to recharge its battery and be powered by them when the circuit is closed. I realize, this is the most difficult one, if even possible, but I'd like an opinion from you guys.

Feature 2: Multi phone Geofencing with paired phone app.
I would like the thermostat to see if either me or my wife gets closer to home and turn the boiler on. I use android, my wife iOS...

Feature 3. Week schedule.
With localization override, if I or my wife arrive or leave home at an unusual time

Feature 4: direct wifi connection.
No hubs, plain 802.11

Thanks a million in advance

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simraba Posted - 11/11/2019 : 01:27:18 AM
Hi Guys,

I realized what I want is impossible because the recharge of the battery of the nest with only wires W and R can only happen when the circuit is closed and not open as I was thinking. Silly me...

I will buy a nest thermostat UK 2nd generation which basically has the same features a 3rd generation.

It will come with a heatlink unit and I will use the existing 220v wires (managed by he heatlink, so downrated to 24v or similar) to feed the nest thermostat itself.

The nest and the heatlink are reasonably close so they will communicate wirelessly (and wired, if there are not too many switches between them)

Thanks anyway!

simraba Posted - 11/07/2019 : 01:51:57 AM

thanks a lot for your answer. Where I live, the UK, most boilers are mains activated. That's the reason why NESTs sold here have the additional "heat link", to deal with mains voltage.

Just for reference, I have exactly the honeywell thermostat depicted in this video:

you can see it at 4:00 with its cover on, and at 4:30 open

it works by shorting the blue and brown wires (220v) to activate the boiler.

Basically, with respect to the UK NEST E, I would like to get rid of:

1. the heat link (as it's just another thing hanging on the wall)

2. the AAA and AA batteries (I'd like instead a battery that recharges while the circuit is not closed, using very little power so the boiler doesn't think it has been triggered, and that powers the thermostat while the boiler is on)

Are you suggesting to combine the relay with a US issued NEST (hence without the heat link). Do I understand you correctly? Does the US NEST works (activates the boiler) by shorting the same 24v it receives power from?

Thanks again for your answer

BLH Posted - 11/06/2019 : 3:20:28 PM
Feature #1. The original thermostat is switching 220 Volts not the low voltage 24VAC found in most systems?
Aube makes a 220VAC controller that has a 24VAC transformer in it. For use in controling a 220VAC system with a 24VAC Thermostst.

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