Thermostat Won’t Change Temperature – Why and How to Fix It

There are several reasons to consider if your thermostat won’t change temperature.

Let’s do some thermostat troubleshooting of common reasons for this issue most likely.

The Thermostat is Locked

Most digital thermostats have a lock function. It’s handy for homeowners that want to prevent kids or others from cranking up the heat or AC.

The next question might be, “how do I unlock my thermostat?” Each model is different, but most are simple to unlock.

Unlock a Carrier thermostat

Press and hold the Mode button while simultaneously pressing both the Up and Down arrow buttons. The Locked icon will disappear in a second or two.

Unlock a nest thermostat

Unlock a nest thermostat

Press the thermostat’s ring, and the Locked icon will appear. Press the ring a second time, and enter the PIN. It will unlock the thermostat.

Unlock a Lux thermostat

Press and release the Next button three times. Then press the Hold button to unlock the thermostat. The same steps will lock it too.

Unlock a Trane thermostat

Press the plus “+” and minus “-“ buttons simultaneously and hold for 3-4 seconds to unlock the thermostat.

Similar techniques work for other brands. You can always search for the thermostat’s manual online, and it should have instructions on what to do if the thermostat won’t change temperature, starting with trying to unlock it.

The Thermostat is in Auto Mode

When you choose Auto mode on some models, you can’t change thermostat temperature. That’s because in Auto mode, the thermostat uses pre-programmed temperature ranges. This is true, for example, with most Lux smart thermostats. Lux says, “If your thermostat is in Auto mode, Heat or Cool modes will be automatically activated within the range of your heating and cooling schedules. You may notice that on the website and mobile apps you can’t make any temporary changes to the current Set Temperature.”

You’ll have to switch the mode to Heat or Cool/AC in order to manually override the programmed temperature.  

The Thermostat Needs to Be Reset

Does it have a reset button? Try pushing that. Sometimes it’s not that easy, and you have to use a thin wire or straightened paperclip to push into the reset hole.

The Installer Set High or Low Temperature Limits

Many thermostats can be programmed with high or low limits, so once set to that point, the thermostat won’t change temperature any further.

Why would an installer do this? Because they didn’t want the system to work harder than it should. A properly sized HVAC system won’t heat your home above 85 or cool it below 55. The system would have to be much too big to achieve those kinds of temperatures.

The Batteries Need Replacing

Occasionally, low battery power will lead to malfunctions in a thermostat including making it so that the thermostat won’t change temperature settings when you want it to.

The Upper or Lower Temperature Setting Is Reached

Most thermostats have a set range of about 40 to as high as 99 degrees Fahrenheit. If for some reason, you’re trying to set it higher or lower, it won’t change temperature from the low or high setting.

The Thermostat Needs Cleaning

Is the thermostat in a dusty area? Remove the cover to look for dust. Blow it out of the thermostat or gently brush it with a soft-bristled, small paint brush to remove the dust.

The Thermostat is Broken

Before calling it a lost cause, check the thermostat manual. If you don’t have it, search online by the brand and model – whatever information you can locate on the thermostat or inside the cover. Search the manual for the thermostat troubleshooting section to see if this issue is discussed along with a solution for fixing it.

If you decide to replace your thermostat, consider our latest Thermostat Buying Guide with a basic overview of thermostats, various types to consider including programmable and smart thermostats plus links to our reviews of popular brands like nest, ecobee, Sensi, Honeywell, Lennox, Trane, and more.

Related Article: Thermostat Not Reaching Set Temperature? 3 Common Causes

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

2 thoughts on “Thermostat Won’t Change Temperature – Why and How to Fix It”

  1. Newly installed AC. Temp is set on 72. The room temp is also read as 72. It never changes. How does the AC know when to come on and off? It seems to be working fine but why does the read out say 72 and 72? I am perplexed.

  2. My thermostat is programmed to the temperatures I want and at the right times, (68°) but once I walk away it goes right back to 75 and when I go to turn it down by using the arrows, it suddenly goes to 85. It won’t set and it’s very frustrating as it’s too Smokey out to open windows.


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