One way to check for thermostat calibration issues is to place a room thermometer a few inches from the thermostat and wait 15 minutes. The readings of both shouldn't be more than 1℉ different. If this is the case, then it's time to correct the issue.
To do so, locate your home's thermostat and tape an accurate thermometer on the wall next to it. Wait 15 minutes and check the temperature reading on both devices. If your readings are three or fewer degrees apart, you should be good to go.
At the heart of your thermostat's functionality is its temperature sensor. 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.
The best way to check is to get a thermometer and place it near the thermostat for a few minutes and see if the temperatures read the same. If they are off by more than a degree or two I would have the thermostat replaced.
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.
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.
Standard thermostats: Enlist a friend or family member to assist, Position one person by the thermostat and one person by the furnace. Slowly turn the thermostat from off to heat and increase the temperature. Both the thermostat and furnace should make a sound.
Try checking the circuit breaker box or replacing the batteries. Bad wiring: The thermostat may be unresponsive if the wiring has gone bad. Remove the cover and check inside for loose, detached, or corroded wires. If you spot any problems, contact an HVAC technician for assistance.
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 you're cold even though your thermostat indicates you shouldn't be, your furnace likely isn't the problem. In most cases, it's working just fine. It's your home that needs attention. Lack of insulation, severe air leakage, and/or unbalanced ductwork are frequently to blame.
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.
Ice water method to check thermometer accuracy:
Add water to the top of the ice and stir well. Let stand for 3 minutes. Place the thermometer stem at least 2 inches into the ice water. The thermometer should read 32˚F after 30 seconds.
Thermostats can lose calibration over time from being accidentally bumped or from dirt accumulating. An improperly calibrated thermostat can cause discomfort because it's not heating your home accurately.
On average, most thermostats last about 10 years, depending on the model, usage, and proper maintenance. However, many people decide to replace their unit sooner to take advantage of new energy-saving technologies.
Yes, many smart thermostats are designed for DIY installation, and manufacturers typically provide step-by-step guides and videos. However, if your HVAC system is older or lacks proper wiring (like a C-wire), the installation might become more complex, and you may need professional help.
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.
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.
While there is a small chance that there is an issue with the running temperature of your engine, by far the most common issue with trouble code P0128 is a faulty thermostat. The exact location of the thermostat and issues related to a damaged thermostat may vary depending on your vehicle.
If the computer detects that the engine is heating up too much, the performance settings will be adjusted to prevent overheating. One of the very first indications that you might have a faulty coolant temperature sensor is when you notice a drop to your fuel economy.
Get an Indoor Thermometer
Another way to test your thermostat is to use a thermometer. Place the thermometer in the room and turn on the AC. After a few minutes, check the thermometer to see what temperature it's reading. The temperature should be lower than when you started.