I installed two digital “set back” thermostats this week in our house: they automatically turn the temperature in the house down at night and up in the morning. The packaging claims 30% energy savings are possible, so it seemed like a good investment, to say nothing of a way of using less oil.
One confusing thing: the instructions, which are quite complete, talk at some length about the need to “label the existing wires with included labels” before disconnecting the existing thermostat to ensure the wires can properly be routed to the new one.
My problem was that the existing two wires didn’t have labels. So I didn’t know where to route them on the new thermostat. Fortunately, in the Professional Reference Guide for the new thermostat, I found the following:
When the thermostats relay (switch) connects RH to W, the heat comes on. If the heating system already has a thermostat connected, use the same two wires that were on the old thermostat. When there are just two wires, there is no polarity, i.e., either wire can go to RH or W.
And in the manual for the old one, I found that, indeed, I had two wires, one RH and one W.
So I just wired one wire to the RH, and one to the W. And that worked.
We’re now 16.5 Celsius at night, and 19 Celsius in the morning.