The Room Temperature and Setting Don't Match If, no matter how often you set the thermostat, the setting and room temperature never match, the unit has likely lost accuracy. The cause may be a calibration issue. Or, the unit may have a wiring problem affecting its function and power supply.
If both your thermometer and your thermostat display the same temperature reading, the thermostat's accuracy and efficiency are good. A difference of 3 degrees or less is generally nothing to worry about. If the readings are different, there is likely an issue affecting your thermostat's function.
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
One of the most common reasons that your thermostat is incorrectly reading your home's temperature is that the temperature sensor is malfunctioning or has failed completely.
A common oversight for a thermostat showing the wrong temperature is the state of its batteries. Dead or low-power batteries can lead to inaccurate readings. Simply replacing the batteries might restore your thermostat's accuracy and functionality.
Dirty or worn flame sensors, blower motor problems, clogs in the condensate lines, and electrical issues are some of the many problems that can leave your HVAC system failing to deliver the temperatures you've programmed in your thermostat.
The calibration screw is typically located in a curved piece of metal. First, remove the control unit from the wall mounting and then locate the screw in the back. Turning it back and forth opens the contacts. Once you feel the setting is correct, turn the calibration screw again to close the contacts.
If the temperature is set to 74°F but the thermometer shows 78°F, you will have to recalibrate the thermostat to account for this 4-degree deviation. Even with older AC units or furnaces, you might have to recalibrate your thermostat from time to time.
Clean the Thermostat
Sometimes, when the room temperature doesn't match the thermostat setting, the problem could be dirt buildup on its interior parts. A dirt coating around the inner components may create excess heat and cause the thermostat to give the wrong readings.
Another problem that can cause your house to be hotter than what you've set the thermostat to is if your home's HVAC system isn't sized properly. An HVAC system that's too large for your house will cool your home unevenly. It will only cool some rooms off and then shut off versus cooling down the entire house.
A mismatched thermostat can damage the HVAC system and the electrical system. The clash between the instructions from the thermostat's computer algorithms with the HVAC system can harm components. (And if you add in a possible wiring error, things get even worse.)
Using a small screwdriver, gently turn the calibration screw or move the adjustment lever until the thermostat's temperature reading matches the thermometer's reading. Make minor adjustments and allow time for the thermostat to adjust to the new setting before rechecking the temperature.
Rectal temps are the most accurate. Forehead temps are the next most accurate. Oral and ear temps are also accurate if done properly. Temps done in the armpit are the least accurate.
After taping the thermometer to the wall, wait for 20 to 30 minutes and then check both the thermometer and the thermostat to see what the temperature reading is on each. Ideally, both will show the same temperature, but a small difference between the two is also fine.
A dirty thermostat sensor will send the wrong readings to your heat pump or furnace. This can lead to that imbalance between the numbers the thermostat is showing and how you feel inside your home. Thankfully, this is an easy fix. You only need to clean the thermostat.
For many of us, 70 degrees is the ideal indoor temperature, but when it is close to 100 degrees outside, your AC unit will be working quite hard to meet these expectations. Consider setting your thermostat at 75 degrees to 80 degrees in your home if the outside temperature is approaching triple digits.
If your thermostat is not reading correctly, it might be due to a dirty or faulty sensor. A quick fix could be to gently clean the sensor with canned air to remove any dust buildup. However, if problems persist, replacing the thermostat could be the next step.
U.S. Department of Energy research suggests that setting your programmable thermostat to 78 during the summer months is the best way to save money on your cooling costs while maintaining a comfortable temperature.
A thermostat can be recording the wrong temperature for a variety of reasons: Your thermostat's sensor is malfunctioning. In some cases, a sensor can be recording the wrong temperature. A simple recalibration can often do the trick.
An uncalibrated thermostat can cause your HVAC system to work harder than necessary, leading to high energy consumption and more-than-usual wear and tear. If energy bills start increasing without any corresponding change to outdoor temperatures or utility pricing, your thermostat may be due for calibration.
One easy thing you can do to check the accuracy of your thermostat is to do a temperature check. See what your thermostat reads. Then use a portable indoor thermometer to compare the temps. Another good way to do the temperature check is to download one of the many free apps that allow you to check indoor temperatures.