What should I do if my thermostat keeps changing or forgetting settings?

What this symptom usually means

When a thermostat keeps changing its own temperature setting or forgets programmed times, the problem is usually in the control itself rather than in the furnace, air conditioner, or heat pump. This symptom points to commands being overwritten, memory being lost, or power to the thermostat dropping just long enough to reset part of its programming. That is different from a thermostat that is blank, unresponsive, or reading the wrong room temperature, because here the key clue is that your settings do not stay where you put them.

What you can observe to narrow it down

If the temperature changes happen at the same times each day, such as every morning at 6:00 or every night around bedtime, a schedule or learning mode is the leading suspect. If the thermostat forgets the time and date, loses Wi-Fi names, or goes back to factory-like defaults after a power flicker, battery or low-voltage power loss is more likely. If the setting changes only when someone arrives home, leaves home, uses a phone app, or talks to a voice assistant, look for geofencing or automations. If changes happen randomly with no pattern and no power outage, the thermostat itself or its wiring is more likely at fault.

One safe step that often separates user settings from hardware trouble

Set the thermostat to permanent hold, manual, or run-without-schedule mode, depending on the model, and replace the batteries if your thermostat uses them. If the setpoint stays steady for a full day after that, the issue was probably scheduling, learning, or a remote automation rather than a failing control. If it still changes temperatures, loses the clock, or forgets settings after batteries are replaced, that points more strongly to a power problem, wiring issue, or bad thermostat.

What a technician usually checks on this call

On a service visit, the technician typically starts at the thermostat menu history, programming mode, and connected app settings to see whether a schedule, recovery feature, demand-response event, or integration is issuing commands. Then they verify battery condition if applicable, measure 24-volt power between the thermostat terminals, inspect the R and C connections, and look for intermittent voltage drop or a loose sub-base. If the thermostat repeatedly reboots, loses time, or will not retain settings after power is confirmed stable, replacement of the thermostat is often the practical repair.

What affects repair cost

Cost depends on whether the fix is a settings correction, wiring repair, transformer-related low-voltage issue, or thermostat replacement. A basic diagnostic and reprogramming visit is commonly at the lower end, while tracing intermittent control wiring takes more labor. In 2025-2026 US markets, thermostat replacement often runs about $173-$652 for many standard models plus labor, while premium communicating or smart thermostats can be several hundred dollars more. If the problem comes from a low-voltage power issue in the air handler or furnace control circuit, the final price depends on what component is interrupting power.