Inaccurate Smart Thermostat? Here’s What to Do

Inaccurate Smart Thermostat

Saving money on electric bills is a task that everyone wants to accomplish. With new craze over smart home technology having an inaccurate smart thermostat is not helping achieve the money-saving goals. If you do have an inaccurate smart thermostat, here is what to do to troubleshoot it. 

What to do about an Inaccurate Smart Thermostat:

  1. Check the accuracy with a thermometer
  2. Check the installation location of the thermostat
  3. Check the wiring
  4. Check the battery (If Equipped)
  5. Add extra sensors

Having an inaccurate thermostat can be frustrating. A few troubleshooting tips can get you back in the green with saving money on your electric bills. The most common problem is the placement of the thermostat itself, and worst-case scenario, you can have the thermostat wiring re-routed to fit your home.

Also read: Do smart thermostats require WiFi

As an affiliate, I may collect a share of sales or other compensation from the links on this page.

What to Do about an Inaccurate Smart Thermostat

You are going to want to check several different aspects, including placement, the sensor, and maintenance. After systematically checking the location, and sensors then you are going to want to make sure that the warranty is still valid. Most thermostats will come with a manufacturer’s warranty against defects.

Place the thermostat in an area that is used frequently and away from anything that can cause a misreading. Getting some accessories and connecting them can also improve the accuracy of your smart thermostat.

Sometimes sensors can go out, with age or improper placement. The best way to check the sensor is to place an accurate thermostat next to your smart thermostat and compare both readings. Using mercury, only an indoor thermostat or a digital indoor weather station can help compare for a precise reading.


Placement of your smart thermostat affects the temperature reading. You want to make sure that the Thermostat is not in direct sunlight for the most accurate reading. Having the thermostat in an area that has constant temperature changes, then it can be challenging to get a precise reading.

Keeping your thermostat away from windows and doors that have a draft will help ensure the thermostat is reading correctly. The wind draft can cause a change in temperature in that specific area of the house, creating a misreading.

Try to place your thermostat in an area that is not prone to heating from appliances. Setting your thermostat next to a lamp, the heat from the light will also be picked up by the thermostat. Ideally, you want to place your Thermostat in a neutral area of your house.

Make sure that any materials do not obstruct your thermostat. Placing a bookshelf in front of the thermostat can cause a misreading, and setting a thermostat in a room that rarely can also create a misreading on your thermostat.

Also read:  Is a Roomba Worth It?

Bad Sensor

It can also be a power issue meaning that the C-wire or standard wire is not present or not connected properly. If you have a smart home thermostat that is Zoned, then you want to check the zoning settings first before re-wiring anything.

Adding additional sensors is an excellent way to create an accurate reading in the home. The Thermostat reading may be accurate, but due to the size of the house and the location of the thermostat, the temperature reading is not correct.

The sensor may not be defective; the thermostat could need some new batteries if you have the type of smart thermostat that takes batteries.

Another issue that gets mistaken for a bad sensor is the setting. Some thermostats have a fan only setting, usually indicated by the on/auto switch on older wired wall versions.  This setting allows you to run the fan only, and not turn on the A/C itself. It can be easy to confuse on a smart thermostat for turning the A/C on instead of only using the fan.

Related article: Do Smart Thermostats Work with Boilers?

How To Tell If the  Smart Thermostat is Not Working Correctly

When your thermostat says that it is 78 degrees in your house, and your freezing, it seems as though the thermostat may be reading incorrectly. There are many things to check before assuming that it is not working.

Some things to check to see if the thermostat is working:

  1. Temperature variance can be adjusted 1-3 degrees in most settings
  2. Check the Wi-Fi connection
  3. Turn the heater on and see if you have hot air blowing out
  4. Turn the A/C on for a few minutes to see if you have cold air.
  5. Take off the cover to see if any componats do not look right.

After checking for visible signs of wear and tear then you want to move forward and complete the maintenance on your system. The misreading could be something as simple as a dirty air filter.  You may need to place a wi-fi extender near the thermostat, or you may need a new thermostat entirely. This initial assessment will let you know where to start looking.


Changing out an old air filter is going to be the first maintenance item on the list. Checking the batteries, and the alignment of the thermostat installed can make a difference in the temperature reading. If you have a thermostat that is still using a mercury setting inside for detecting the temperature, it needs to be level.

Also read:  Does Blink Require a Subscription?

There is a mercury tube inside that, if tilted, can cause the temperature reading to be off. Check with the manufacturer or an HVAC professional to determine if your thermostat has one of these types of sensors.

Clean your vents and perform your regular maintenance on your system annually. You can call a professional or do the maintenance yourself.

Steps to maintaining your HVAC Central A/C Unit:

  1. Turn off power
  2. Clean the fan
  3. Unclog the evaporator drain
  4. Clean the fins
  5. Straighten bent fins
  6. Change indoor filter
  7. Clean off heating elements
  8. Clean off evaporating coils
  9. Clean around the Unit
  10. Make sure the unit is level
  11. Return power to the Unit

Do not use a power washer to clean, and don’t spray the A/C unit down with a hose in an uncontrolled manner. These methods can cause damage to you’re A/C unit.  You can get a good A/C spray cleaner and an A/C cover for maintaining the Unit.

Check the Wiring

The Wiring in the unit may be old or outdated, and if the correct amount of current is not reaching the thermostat inside, then the reading may be displayed incorrectly. Remove the cover and check the wiring with a Voltmeter to make sure that the correct current is flowing into each section.

Check to make sure that the wiring is connected correctly; each system has anywhere from 3-10 wires with different purposes for each of them.

Color Type Information
Blue Common wire Available on most units
Green Fan Required
Yellow Compressor Required
Red Power 24V Required Also See Red C/H
White Heat Required for combination units
Red C Cooling power Can be bridged with Red H
Red H Heating power Can be Bridged with Red C
Orange Wire Furnace Takes the place of white wire

Some wiring may be faulty, which could also lead to a loss of power within the system. For low voltage systems (25V), a shortage in one of the components has a substantial effect on the performance. You should replace necessary wires accordingly, and avoid splicing thermostat wires if possible.

If you need to replace a wire set, the easiest way to replace the set of wires would be to tie a string to the old ones and connect the line to the new wire set. Then Pull the old wire set from the A/C unit through the wall until the new wire set reaches the A/C unit.

Final Thoughts / Conclusion

Most home improvement tasks do require some technical skills to accomplish. The thermostat is an easy installation that only requires a few tools.

It would be best if you never took on a job that you are not 100% confident that you can do on your own. Depending on the layout of your home, and the locations of the thermostats and sensors, upgrading can either be easy or an extremely challenging task.

In the case that you are unsure you can accomplish the fix safely, I would always seek the help of a local contractor to assist you.