I have inherited an electric boiler for heating water in pipes running through the house.
The existing thermostat is a very old and very simple mechanical one. I want to install a more recent thermostat, ideally a 'smart' model that 'learns' over time.
Here's a picture of the wires going into the boiler from the thermostat (the bottom 4).
S2 are the 4 wires that appear to go up to the thermostat.
TH wires go to the thermostat,
S2 are going to an outside sensor.
The only one I recognize is the unconnected 'C' ('common'), which means I need to run it up to the thermostat in order to install a newer "smart" thermostat model. Is this assumption correct?
Also what are all the unconventional wire labels? None of them are what I commonly see in articles on the net (
Y/Y2). How do I reconcile them with labels in instruction manuals for recent thermostats?
Update 1: Boiler model is Dettson HYDRA15-E2401M-C (manual PDF). Turns out
TH stand for "thermostat", that's the first 2 wires. The other 2 (
S2) refer to
"modulation" outdoor sensor in manual and are also going up to the thermostat.
Update 2: after opening the Honeywell thermostat. The 2 wires are hooked up directly to the boiler
TH connections. Wire colours are not continuous (white and red at the boiler vs. white and black at the thermostat). What do the
R mean on the thermostat screws?