I'm trying to replace an old manual thermostat with a new digital thermostat for my line voltage baseboard heaters. If it's important, this particular thermostat simultaneously controls two separate baseboard heaters on opposite sides of a large room.
The hole in my wall has 6 wires, 3 black and 3 white (and a 7th ground wire, which I am ignoring for the purposes of my question). The wires come in black/white pairs from three corners. I am naming these corners α, β, and γ (alpha, beta, gamma). Thus the six aforementioned wires are αb and αw, βb and βw, and γb and γw.
The old double-pole thermostat seemed to function correctly. The wiring was as follows, where parentheses indicate a single solderless connector:
(L1, αb, γb)
(T1, βb)
(αw, βw, γw)
L2: unused
T2: unused
I thought it was strange that L2 and T2 were unused. When I wired my new double-pole thermostat I did as follows:
(L1, αb, γb)
(T1, βb)
(L2, αw, γw)
(T2, βw)
However, this new thermostat does not appear to be working. Did I wire it correctly?
I hope my notation is clear but I'm happy to edit if necessary. Thanks in advance for your help; much appreciated!
Best Answer
It sounds like the a-cable and the y-cable do indeed go to the two controlled heaters. So we know for sure those should stay together.
That would make the B-cable the supply.
Your old thermostat was passively powered. It either connected sides together, or it did not. As such, it didn't matter which side each one connected to, there was no input or output side.
This new switch needs power. It needs power all the time. So it won't do if it severed power to itself when turning off heat.
Instead of trying to wire this thing in one swell foop, you should do it in steps.
Hook up power to the thermostat first. Get the thermostat to power up and pass a diagnostic.
Since we're fairly sure power is the B-cable, figure out which wire sets (L or T) need to connect to that.
Once the 'stat powers up, the rest is straightforward.