Thermostat Not Working

When this becomes an emergency

• The screen is dark, or it lights up and then drops out again a moment later.
• Buttons respond but nothing downstairs ever starts.
• The reading is several degrees off from a thermometer sitting beside it.
• It reverted to defaults or dropped its schedule on its own.

What a pro does

A thermostat is a switch and a sensor, so troubleshooting splits along those lines. On the switch side, a tech verifies the low-voltage supply, then jumpers the heat terminals at the equipment to see whether the system responds to a direct call. If it fires, the fault is upstream in the control or its wiring. If it doesn't, the thermostat was never the problem. Wiring is where older houses get interesting, because the cable running up from the basement is often decades old, stapled through joists, sometimes spliced somewhere nobody documented, and a conductor nicked during a remodel produces exactly this intermittent behavior. Smart thermostats add their own wrinkle when a system has no common wire and the unit tries to steal power through the heat circuit, which browns it out mid-cycle. Sensor problems are usually placement instead. Sitting on a cold outside wall, in a draft from an old window, or above a register all skew the reading badly.

Frequently asked questions

Thermostat Not Working?

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