Nest thermostat with Baxi caldaia murale – natural gas heater with Perri Termostati a 220 240v thermostat

edited on Feb 12th 2013 – futuristic views included

following a request from Massimo a Nest thermostat potential adopter in Italy,

I am trying to assist him in what could be the ad-hoc wiring of a Baxi gast heater mated to a Perri Termostati, a 220 240 thermostat.

the two thermostat wiring options are shown below:

perry thermostat TE120 TE121 TE122 TE123

elettronic termostati perry italia

in my opinion, the “red” boxed wiring (if compatible with the Baxi heating unit) is preferred.

Massimo having now confirmed his wiring is not the red box above, but rather the separate circuitry of supply and dry switch as shown below:

…I am starting to think about how is the actual wiring done at the heating unit level – my point being that I do not believe the actual wiring per Massimo’s feedback

is as shown below (from the Baci user manual):

section added on Feb 12th 2013.

so given the status reach previously, here is below what I would advise one may want to setup in order to make the Nest Thermostat work with a heating system not providing both line and neutral.

Please note that my preliminary conclusions are that the RC840T is not per-say compatible as-is.

baci thermostat nest wiring prosposed

Now if we want to get a notch more futuristic and ask Nest Lab a serious ease of implementation with “most” heating systems in EU (at least the ones working on 220 240 volts), here is what a good step forward would be….

I just want to point that this version of Nest thermostat does not appear to exist today, but it should not be that complicated to roll out for the European market.

what do you think? Do you concur?

missing 1 wire from my gas heater to my Aube RC840 to finish off Nest Thermostat wiring!!!

Dear all,

have verified in full my previously recommended wiring  earlier this week – having a 3-wire (220 240 Volts) cable running from my gas heater, to my RC840, and 3-wire from my RC840 to my nest thermostat.

While doing this, I have actually used this to let me Nest get fully charged, updated to the latest software, and exercised it a bit.

A few comments for those who go thru this process:

1. it took a few hours to get my nest battery charged up to at least 3.7V
2. note that in between it may (at least mine did) reboot a few times – realizing it does not have enough energy to run wifi (required to get the update done – have no idea about the size of the download by the way, do you?)
3. 3.7V is critical as it is the minimum Nest needs to be able to launch software updates
4. once update was done, an easy trouble-free process, I was able to fully control my nest via my Ipad

I live in an 1930s building, and our apartment got renovated to the current Electricity standard a few years ago (meaning I have a decent amount of extra wires running thru the various electricity access). Frustration rose when I realize I did NOT have a 220 240 Volts with 6-wires but 5-wires!

This means I can’t properly wire the Ns/Ls/Lr from my heating unit to the RC840T (I had planned to locate it near my fuse box – opposite from my heating unit).

So I have paused my installation – and – it looks like the only alternative is to change the heater supply cable and upgrade it to a 6-wires one.That’s assuming of course, I have room to retrofit it!! If you can think of anything else to do… please chime in now!!

In any case, I have updated and confirmed now that the diagram below is fully working.

if you can’t figure out how is laid out the apartment and how the wiring has to run, I will draw up a schematic of the flat and the way the wire will be running thru.

Electrical wiring of my previous 220 240 Volts (high voltage) thermostat to my gas heater

default wiring for high voltage thermostat

to all, above is a drawing of my previous configuration using a “2-wire” thermostat, high voltage that is 220 240 Volts, directly connected to my gas heater.

couple of key points:

#1 the thermostat had batteries internally used to trigger the “dry switch” (now on the drawing).

#2 upon “heat” command (ambiant temperature below target) the “dry  switch” basically closes the electrical path between Ls and Lr

#3 once Ls and Lr are connected together, this triggers the heater (gas + circulator)

#4 Ns connector is shown although not used in this configuration since thermostat operates from its own supply (internal batteries)

electrical schematic of nest thermostat with 220 240 volts heating system

nest thermostat 220v europe

following request for clarification,

here is my understanding of how this works, and particularly what is the RC840-240T doing for you.

#1 RC840T-240T is overkill – this box is designed to drive directly an electric heater (2kW or so…). this means the relay in this box can carry a lot of current

#2 note this device is not approved in Europe, probably because of 50Hz and 220 240 Volts (versus 60Hz and 110 Volts), so a new certification would be required.

#3 and I Will pause here, I have a doubt about the need (or not) for the C wire to be connected honestly, so I will investigate and report back once I have a chance to spend more time.

the natural gas heater and its nest access

my heater is a basic elm leblanc acleis 23kw natural gas.
it works on 220 240 volts and is currently trigger by a 2-wire high voltage thermostat.

here is the front of the heater

with the cover removed

the Aube/ RC840 box will connect instead of the grey and black wires.
those are precisely hooked to Ls and Lr connectors.

it is worth noting that I will leverage from the Ns connector which on a high voltage 2 wire thermostat is not used.

received my 5x units of 220 240 Volts 24 Volts converter (with relay built-in)

I had initially the “ambition” to build my own transformer/relay in a box…
it turns out that both work and family activities forced me to look for a plug & play system.

I have ordered 5 units of this Aube RC840-240. Note those aren’t certified to operate in Europe… so you cannot supposedly buy them in Europe (have discussed with Aube themselves via emails and they refused selling me those).

So, I ended up buying those units from a 3rd party shop in California, they have arrived this last week end.

yesterday evening, at least to verify the concept would work, I plugged my current 2-wire “high voltage” thermostat thru this RC840-240 unit… and it works great. Picture and block diagram to come soon.

essentially, I am one step away from having my Nest wired to my heater a ELM Leblanc (natural gas) unit. Note the system I have actually selected could work as well on Electric heater systems with some cautious calculation.

Stay tuned.