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.
Checking the calibration of your thermostat is easy and should be done once a year, generally in the fall. 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.
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.
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.
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.
Use the manual to find the screw for calibration. Turn the screw to match the temperature of the thermostat to the room temperature. Turn the HVAC system and the power back on, and the power. Turn on the thermostat and wait a few minutes for it to adjust to the temperature.
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.
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.
Bring a deep container of water to a full rolling boil. Submerge thermometer stem (including the sensory dimple of a dial stem thermometer) for about 30 seconds — until indicator stops moving. Make sure that the stem does not touch the side or bottom of the container. Check to see that the temperature is 212 F (100 C).
In most cases, installing a new thermostat is a relatively simple do-it-yourself project that can result in improved comfort and convenience and one that can help you save energy.
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.
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.
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.
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.
Replacing a Thermostat. You'll pay between $15 and $300 for the unit in addition to labor ($65 to $100 per hour) to replace an old thermostat with a new one. However, installing a brand-new thermostat is more involved and, therefore, more expensive.
After cleaning the thermostat and making sure it is level, you will then want to use your thermometer to test your thermostat for accuracy again. If the thermostat still isn't accurate and shows more than a 3-degree temperature difference from the thermometer, it means the thermostat needs to be recalibrated.
First, replace the batteries in your thermostat as this is the easiest fix. Then, you should check that your thermostat is level and that all parts of your HVAC system are clean. In particular, look out for dirty air filters, which can be the cause of your thermostat reading the wrong temperature.
Access the Menu: Once the thermostat is off, press and hold the center button on the device. This will bring up the main menu. Navigate to Reset Option: Use the arrow buttons to navigate to the “Settings” option, then select “Reset” from the list. Select Factory Reset: You will see a few reset options.