Hello Pconway,
Thanks for posting here in the Google Nest Community! It looks like you're dealing with a thermostat that has only two wires. This situation often occurs with heating systems that don't require a dedicated cooling wire. The two wires are typically used for heating control.
To help you better, could you provide more details about the type of heating system you have? Knowing whether it's a forced air system, boiler, radiant heat, or another type. In general, with two-wire setups, one wire is for power (usually labeled "R" or "Rh") and the other for heating control (often labeled "W" or "W1"). However, it's crucial to confirm the wiring and compatibility with your thermostat model. Share with us a photo of your current thermostat's wiring.
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I'll look forward to your response.
Best regards,
Mark
