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.