Why Your Thermostat Not Reaching Set Temperature? Causes, Troubleshooting & Fixes

Thermostat Not Reaching Set Temperature

Extreme weather conditions and the thermostat not being able to reach your set temperature can be a terrifying situation. 

So In this article, I’ll explain all the possible reasons for thermostat malfunctioning and how you can resolve them.

Before starting with reasons and solutions, we will explain the types of thermostats because causes and diagnosis can differ according to HVAC models and tiers.

Understanding Different HVAC Thermostats

Programmable Mechanical Thermostats

This is traditional thermostat comes without an LED display unit and basic user settings. These are cheaper, and very few companies still manufacture them because of less demand and age-old technology.

Several states and countries in North America have banned programmable mechanical thermostats because using mercury switches to complete machine circuits.

Digital Thermostats (Non-programmable)

Users can change the temperature manually for desired heat indoors. This system lacks programming and automation, which makes it less efficient.

Digital Thermostats (Programmable)

These are programmable digital thermostats, which means you can schedule time, maximum temperature limit, on/off, etc. The settings changes when you rest them, not by themselves.

Smart Thermostats

Smart thermostats are the most advanced and equipped with the latest tech features for a premium HVAC product experience. Unique features of this type of thermostat are zone control, LED touch screen, Wi-Fi, remotely operable, voice command options, etc.

Reasons Why your Thermostat is not Reaching Set Temperature and Its Solutions

1. Inadequate Size of the Thermostat

Before considering any functional problem, you should check if the house or the area is suitable enough for proper thermostat operation. The HVAC system might be too small to reach all the corners of the home, or the design does not support the desired area. These things need to consider at the time of purchase.


Get a thermostat that covers your complete home. You can consult a local HVAC product supplier or a technician who will visit your home and suggest the required thermostat for the home for optimum temperature all across the house.

2. A Damaged Thermostat Sensors

The sensor adjusts the temperature after measuring weather fluctuations in the surrounding area of your home. If it is damaged or broken, the machine will function abnormally and not perform according to set instructions.

Types of sensors vary according to types of thermostats

  • Mechanical thermostats come with bi-metal strips. Copper and Nickel are bonded together for providing information on the required temperature. Some of the HVAC systems use an alternative sensor known as gas-filled bellows.
  • Digital thermostats, both programmable and non-programmable, use thermistor sensors. It is an electrical resistor that works as a physical resistance during temperature changes.
  • Smart thermostats offer sensors with remote control options supported by Wi-Fi and Web applications.


If the thermostat sensor is damaged or broken, generally, you need to replace it. You can call for professional help or do it yourself.

3. A Malfunctioning Fan

Check your fan; a dysfunctional fan could also be a reason for abnormal behavior of the thermostat. Fan pumps in hot air and pumps out cold air. If it does not work in that order, the indoor temperature would not reach the desired level. In addition, if the fan keeps the pump in cold air, the thermostat will break its balance in the process.  


Switch off the fan for about two minutes after switching off the system. It will resolve the issue for minor glitches. If still persist, call a registered technician for advanced diagnosis and resolution.

4. Frozen Display of Thermostat

Static electricity around your home could cause a frozen thermostat. This is a common problem with smart thermostats, widely used for all HVAC products. The system gets freeze and data could not reach the system, leading to no updates and temperature changes as per set instructions.


Reboot the system, switch it off for a couple of minutes, and re-start. Smart thermostats come with advanced reboot options with a data storage option. You would not experience any data loss, and your thermostat will usually start working.

5. Insufficient Power Supply

If your thermostat is experiencing power interruptions, it would not reach the set temperature. Power supply loss when thermostat screen becomes dark and blank. As a result furnace and condenser also stop functioning.


Reset the power connection and check the screen. Call the experts to repair the system if the screen is still blank and dark. 

If you want to repair it yourself, read the user manual and research on the web. You must ensure the right process for maintenance to reduce the chances of error.

Other Reasons For Thermostat Not Reaching Set Temperature

  • Temperature does not adjust according to the set instructions when the unit does not place properly. Uneven wall, improper pin connection between the backplate and the thermostat, etc., could cause abnormal thermostat behavior.
  • Thermostat performance varies according to a location within the house. You will experience higher temperature if placed near areas that receive direct sunlight, such as large windows, a place full of lights, a fireplace, etc. In the reverse situation, the thermostat provides a colder temperature.
  • Dust and debris can block sensors, and thermostats start malfunctioning. Keep your furnace and thermostat clean to avoid such problems.
  • Improper and loose wiring can also be the temperature adjustment problem.


These are some common causes for the thermostat not reaching the set temperature. We hope our solutions and tips will help you repair your thermostat comfortably. If not, consult professionals for diagnosis and resolution of the problem.

If your machine is old and uses the traditional manual system, there is always an option to replace them with a new advanced HVAC unit.

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