Advice replacing my old thermostat with HestiaPi

Hi everybody!

First of all, I am sorry as this is a very basic question, I did not succeed into finding another post in the forum answering the question I have.

Today I started the installation of my HestiaPi Touch, so far I have removed my old thermostat, successfully configured WPA, and fixed the stunning hexagonal cage to the wall, however, this installation that I believed to be plug & play definitely requires some help!

The thermostat I am replacing is battery powered, it is essentially a contact relay scheduled by a thermistor and a set of profiles that can be configured. The system when on takes care of both the heating and the water, which is always on, recirculating.

Accordingly, at the electrical level we can think of my previous thermostat as a simple relay that opens / closes the circuit that triggers the system as a whole. If I remove this thermostat and connect these two wires, the heating system turns on just fine.

That is what I want to achieve with my HestiaPi, something I believe must be possible. However, it seems like HestiaPi is designed for systems which have 4 wire thermostats… in my case I just have the 2 wires mentioned, between the heating system and the thermostat…

In order to power up my HestiaPi I have wired L and N from the house, not from the system, is this wrong? If this is wrong I am screwed because it seems my setup is different, and it is really afar…

So, my HestiaPi boots and connects to WiFi, I can SSH and tinker. Although, the screen is still white (I have asked about this in another post).

So, where I expected simple terminals for connecting the 2 wires I have for enabling/disabling my heating system as a whole, I am seeing a Water (W) wire and a Heating (H) wire which to me both seem completely different to what I had with my old thermostat.

To my limited understanding, both W and H are different relays, so I do not know how to proceed, shall I install 1 wire to H and the other 1 to W? seems nonsensical I know, as I said both are different relays…

So please, help me see the light! I want HestiaPi to behave like my old thermostat, to be like one simple relay, but with all the cool & hacky stuff HestiaPi offers!

Thank you very much for your help and your time.


Hello Antonio

The systems in Europe at least should offer L and N but as you said it is battery operated it may be possible that the electrician cut down the cost and only passed one wire. That should be the L. You will definitely need both L and N for HestiaPi to power up. You need someone with better understanding on basic electical connections and maybe a test light (tester screwdriver with light).
Once you get L and N there, the other wire you mention should go to H for heating. Make sure you know exactly which is L and which is N otherwise HestiaPi will power up but will not control on and off of the heating. Please get a friend to help as it easy to kill at least a fuse in the best scenario. :slight_smile:
(replying to your other thread about the white LCD)
Let us know how it goes and maybe share some photos if we can help

1 Like


Thank you very much for your response!

Definitelly It looks I am screwed and need help from an expert :crazy_face:, if in the end it is required to wire the two additional L & N wires originating from the system… Sorry for writing such long posts, I am adding extra details in order to see if there are possibilities!

I have 2 wires (black and grey) which originate from the heating system, not 1, thats all my previous thermostat needs in order to activate the heating system. If I remove the thermostat and connect these wires directly then the heating system turns on, as a simple contact relay would do, I have just measured 220VAC for this black-grey connection. The heating system I have manages water independently of the thermostat, I want to use HestiaPi just for house heating.

Two months ago I successfully installed a different 4 wire smart thermostat at a friend’s house in a similar scenario, and only black and grey wires matered for the thermostat, I powered the thermostat from L & N in parallel to the heating system, but I could have had it powered from an indepenendent L & N, a procedure which is stated as supported by its manual, it was a very plug and play experience, but not opensource as HestiaPi…

As far as I know, the internal relay of every thermostat (I have worked with) when powered it just closes an independent circuit which triggers the heating system (black & grey wires or LS-LR / TA / COM-NO). So the input power of the thermostat (be it L & N or even AAA batteries, as in my previous thermostat) shall be independent from the circuit enabled by its internal relay (black and grey wires or LS-LR / TA / COM-NO). Is HestiaPi able to be installed like the other thermostats I worked with?

So right now I have

  • 2 original LS-LR / TA / COM-NO wires originating from the system: 1 black and 1 grey, which carry 220VAC originating from the heating system.
  • 2 new wires I added today, L and N, independent from the system, which carry 220VAC. I am currently powering up my HestiaPi from these new L and N wires.

I hope that by having 1 black and 1 grey is there a way to use the HestiaPi in my setup, probably with the L/N I added alongside.

Thank you very much and sorry for being so verbose.

Best regards,

Can you measure with a multimeter the voltage between L and black, L and grey, N and black, N and grey? 4 measurements that is.
Is the power heating system powered from the same point your house is? Is it a single phase or triple phase?

voltage between L and black: 396V
voltage between L and grey: 230V
voltage between N and black: 230V
voltage between N and grey: 143mV

The power in the house is triple phase, by measuring 396V sounds like two different phases were being mixed between L and black… so I guess the black & grey originating from the system are in one phase different from the L & N originating from the house.

If this is in fact correct, and only if you agree, may the inputs to the board be:

L: black (which comes from the system)
N: N (blue, which comes from the house)
H: grey (which comes from the system)
W: empty (as my system manages water pump autonomously)

removing the remaining L (brown) which comes from the house so as not to ever inject 396V to the system

Thank you very much!!!


Spot on Antonio!
Do one more test though…
Connect a light bulb (or anything really that consumes more than 10W) to Black and N and see if it lights up.
If it does proceed with the wiring you mentioned and yes, remove the L to avoid trouble.

Looking forward to your results!


Looks like I am out of luck!

I have tried a couple of devices and the breakers go down. Any other idea?

I guess if HestiaPi only supports mordern “modulating” heating systems, not legacy on/off heating systems like mine.

Thank you very much!


I was worried this would happen. A last resort without breaking any electrician’s laws here :slight_smile: and making HestiaPi fully working would be to connect the wires coming from your system to different points on the PCB but that would require soldering 2 points and cutting a track of the PCB. If you are willing to do that I will post detailed posts here with photos.
Let us know

Hi Antonio, I’ve modified my Touch PCB to do exactly that, but from a 5V power supply - check out my post here

1 Like