Thermostat Keeps Changing Temperature on Its Own? Here Is Why

A thermostat has two numbers. One is the room temperature it measures. The other is the setpoint, the temperature it is trying to reach. This guide is about the second number changing when you did not touch it.

That almost always means something told the thermostat to change: a schedule, a timer on a hold, a learning feature, a sensor that thinks the house is empty, an app on someone else’s phone, or your utility. Modern thermostats have many of these, and several are switched on by default.

Match what you see to the cause

If the temperature keeps going up by itself

A setpoint that creeps up has a short list of usual suspects:

• In summer, on cooling: an energy-saving mode. Google says that in Eco the system still keeps the home within the “Cool to” and “Heat to” Eco Temperature range, so with the air conditioning on, Eco means a higher temperature than your comfort setting. A utility event does the same on hot afternoons: Rush Hour Rewards adjustments are typically up to 4°F, lasting 3 to 4 hours.
• In winter, on heating: warming back up. Google says some 4th gen Nest Learning Thermostats with Adaptive Eco pre-heat to your comfort temperature within an hour of your return, and Honeywell Home’s early-start feature raises the heat ahead of a scheduled warmer period.
• Small, gradual rises over a few weeks: Google’s Seasonal Savings, offered each summer and winter if you opt in, makes adjustments of typically up to 2°F to your schedule and runs for 3 weeks.
• A schedule or a hold: the same checks as in the list below.

If the setpoint stays put but the room gets warmer than it, the thermostat is not changing anything: see a thermostat that is not working.

The causes, one at a time

1. A schedule you forgot about.Safe check

   Programmable thermostats often ship with a default schedule, and a previous owner may have left one behind. Honeywell Home's T5 and T6 thermostats, for example, can hold four periods a day for each day of the week. Open the schedule menu and read every period. Edit it to suit you, or turn the schedule off if you prefer to set the temperature by hand.

2. A temporary hold that ended.Safe check

   When a schedule is running, a manual change is only a temporary hold. On Honeywell Home's T5 and T6, the screen shows Hold Until followed by the time of the next schedule change; at that time the thermostat goes back to the schedule. To keep your setting, touch the Hold Until message and choose Permanent Hold.

3. Early start.Safe check

   Honeywell Home thermostats have a feature called Adaptive Intelligent Recovery, Smart Response or Early Start. The thermostat learns how long your system takes to reach a temperature and starts ahead of time. Honeywell's example: with a wake time of 6 am at 70°F, the heat comes on before 6 am so the house is at 70°F by 6. The word Recovery appears on the display while this is happening. It is working as designed, and it can be turned off; on a Lyric thermostat the switch is in the app under the gear icon, then Advanced, then Adaptive Recovery.

4. Schedule learning.Safe check

   Google says that with Auto-Schedule or Smart Schedule turned on, a Nest Thermostat E or Nest Learning Thermostat learns from the adjustments you make and changes its schedule to match. If you turned the heat down a few evenings in a row, it may now do that for you. Turning learning off keeps the existing schedule but stops new changes; you can also clear the schedule and start again.

5. It thinks nobody is home.Safe check

   A Nest thermostat can switch itself to Eco Temperatures when Home/Away Assist decides the house is empty, using phone location and the activity sensors in Nest products. ecobee's Smart Away does the same when its occupancy sensor has detected nobody for two consecutive hours during a scheduled Home period. A thermostat in a hallway cannot see you in a home office, and a phone with location turned off does not count. Turn the feature off, or add a room sensor where you actually spend time.

6. A utility savings program.Safe check

   Programs such as Rush Hour Rewards and Nest Renew on Nest thermostats, and Community Energy Savings on ecobee, let the utility or a savings service adjust the temperature at peak times. Google says Rush Hour Rewards events typically change the temperature by up to 4°F for 3 to 4 hours. ecobee says its events happen a few times a year, last no more than a few hours, and that the thermostat first precools or preheats the house. They only apply if someone enrolled the thermostat, and ecobee says participants receive an incentive from the utility. ecobee notes that you can opt out of a single event by setting a hold, and that leaving the program permanently means contacting your utility.

7. The wrong time or location.Safe check

   Honeywell Home lists an incorrect time setting, or an incorrect zip code on a WiFi-connected thermostat, among the reasons a thermostat does not follow its schedule. Check the clock, especially after a power cut or a change to daylight saving time.

8. Someone else.Safe check

   Anyone with the app on their phone, a voice assistant routine or a smart-home automation can change the setpoint. Check who shares access to the thermostat account. If the changes come from the wall, most thermostats have a screen lock; Honeywell Home's T5 and T6 offer a partial lock and a full lock.

What the features are called, by brand

Names change between models and app versions, so follow the labels on your own screen.

When it is a real fault

A few signs point to the thermostat or the system instead of a setting:

• The setpoint jumps to an extreme value at random, with no schedule, hold or program active.
• The screen goes blank and restarts, then comes back with default settings. That is a power problem; see a thermostat that is not working.
• The setpoint holds steady but the system turns on and off every few minutes. That is covered in a furnace that short cycles.

If you have turned off every feature above and the setpoint still moves by itself, contact the thermostat maker’s support with the model number. They can usually see what triggered each change.