How to connect 2 Heater wires with only 1 terminal block slot?



After letting my hestiaPi in a drawer for a few mounths,
I now need it to control my heater. Winter is coming !

But I am puzzled about how to connect my HestiPi to my heater.

I have a HestiaPI Touch V4.0. The EU version with a 4 slots terminal block.
The 4 slots are:

  • H
  • W
  • AC L
  • AC N

I suppose I should connect the main 220v AC current to “AC L” and “AC N”.

Know I have a Heater that is commanded by 2 wires.
I suppose these 2 wires should be connected to the relay on the HestiaPI.
But there is only 1 "H " slot !

I couldn’t find the Heather wring information on the HestiaPi documentation.

Must be something basic I’m not understanding.

Any idea ?



This model supports one contact systems. It returns L (mains Line) to either H or W. Can you check if your system can be adjusted on the furnace side to support just one line?


Thanks for your reply.

I have also found today a related topicon this forum:
The problem wasn’t solved in that case. Altought it was with a triphase installation, wich is not my case.

Installation and maintenance manual of my Furnace (Wiessmann Vitodens 100-W) shows 2 wires for control.
I doesn’t provide more information.
As I understand it, the thermostat should shortcut the 2 wires when requesting heating to the furnace.
And should unconnect them when not requesting heating.
So the furnace probably provides its mains Line on one of the two wires and check if it gets the same voltage level on the other wire.

My concern about connecting L (mains Line) to the furnace is that the furnace itself may not be connected to the same mains Line than the HestiaPi.


Absolutely. Dont simply connect L to the the 2 wires. The safest would be an additional relay outside HestiaPi that will be triggered from the heating pin of the HestiaPi and will short these 2 wires. Otherwise get a professional or someone who is 100% sure of what he is doing and suggest another solution depending on your wiring.