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AC T-Stat Won't Accept New Lower Setpoint
Honeywell RTH221B1021. Installed 2012. The other day I decided to lower the setpoint from 80 to 78 degrees. T-stat still maintains 80. I checked the batteries which are OK. Can't figure this out unless this t-stat has some kind of faulty resistor etc. Never had a problem before. I will try other T-stats I have lying around if this thread doesn't come up with some solution that I'm missing. I see it has three wires.