Upgrading thermostat. Confused by wiring


Old 12-23-20, 08:00 PM
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Upgrading thermostat. Confused by wiring

I'm looking to update two outdated analog thermostats. We have two thermostats, one for each baseboard heater upstairs. It's all powered by a double pole 240v 20A breaker. From what I can tell, the heaters / thermostats are the only thing on that circuit.

Behind the nursery thermostat, there were two sets of wires coming into the box. One was the 2 line and the other was the 2 load going to the nursery baseboard heater. I easily replaced this one with a MYSA thermostat.

The one in our master is a mystery to me. There's only 1 set of 12/2 (or 10/2) wire running into the box behind the thermostat and it's still hooked up to a single pole analog thermostat (black to black on thermostat and white to red on thermostat).

According to the MYSA app / installation guide, it doesn't look like the MYSA is compatible with this setup. That's fine, but we would still like to update to something digital and controllable. Are there any options out there for this setup without rewiring?

I drew up a diagram of what I've found so far, in both the thermostat boxes and running into the baseboard heaters themselves. Each baseboard heater only has a single 12/2 (or 10/2) wire running into them for power.

I'm lost as to how this circuit works. I've been through, mapped and replaced all switches and outlets in the house (from beige to white), so I'm fairly certain there's no other wires related to this circuit elsewhere.

How could this work without maybe a hidden junction box buried in the walls?


Old 12-23-20, 08:13 PM
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Yes..... you are missing something.

If the nursery and the master are on the same 2P breaker..... you're missing the place where the supplies combine.

Be sure to check both ends of the heaters.

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