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How To Troubleshoot My Aprilaire Thermostat

Aprilaire has a range of Thermostats that allow you to control your home’s temperature, humidity, and air purity. Using the smart app on your phone gives you total control of the air quality in your home, even when you are away.

In addition to controlling air quality, the Aprilaire thermostat will also provide alerts about changing filter schedules and water panels.

Troubleshooting your Aprilaire Thermostat is a simple matter of following guidelines to test and correct the various functions of the thermostat. While the manuals for the different models will provide detailed operational steps, here, we will go through ways to fix malfunctions in the system.

We have made it easy for you to identify problems with your specific model as we deal with each model separately. The individual models’ manuals suggest some checks, so checking the manual is always a good starting point.

Thermostat model 8355 Troubleshooting Guide

ProblemSolution
 1. Unit does not switch on.Check that the unit has a power supply. Check the fuse and replace it if broken. A 3 Amp fuse is required. Check that the compressor short cycle protection feature is not operational. You can override this feature by pressing reset. Note that the short cycle protection feature is there to protect the compressor, and by pressing the reset button, you will also erase any programming that has been entered.  
2. Display is blank, or Display flashes or ‘LO BAT’ is on. This indicates that the batteries need to be changed. 
3. Incorrect time display.    To change the time, press the ‘P’ button followed by the up or down arrows, once the correct time is displayed, press the P’ button. 
4. Thermostat turns on, and off too often.   The default setting is for the thermostat to activate if the temperature changes by one degree. You can adjust the programming to activate the thermostat once the temperature changes by two degrees.
5. Thermostat does not follow the Program Schedule. Here you will have to go through four possible solutions. The thermostat is in manual mode and needs to be switched to program mode. To do this, press the ‘P’ button until the PROG position displays. Check that the thermostat is not programmed in the ‘heat’ or ‘cool’ position. Check that the programming times are correct. Make sure you have corrected for ‘am’ and ‘pm.’ Check that the program day is correct. Remember, Monday is given as 1, Tuesday as 2, and so on. 
 6. No Heat or No fan Check that the switch is on. Check That the door panel has been correctly closed. Check that the wiring is secured and that no wires are touching. Ensure the power supply has been disconnected before checking the wires to avoid injury

Thermostat Model 8620 troubleshooting guide.

ProblemSolution
1. Unit does not switch on.Check that the unit has a power supply. Check the fuse and replace it if broken. A 3 Amp fuse is required. Check that the compressor short cycle protection feature is not operational. You can override this feature by pressing reset. Note that the short cycle protection feature is there to protect the compressor, and by pressing the reset button, you will also erase any programming that has been entered. 
2. Temperature settings do not changeEnsure your heating and cooling temperatures are set to the correct ranges. The right heat range is between 40 and 90 degrees F, and the cooling range is between 50 and 99 degrees F.
3. Heating system is on but the screen does not function.This indicates a fault with the wiring. If there is a power supply between the common (24VAC) and the heat terminal; the problem is with the heating equipment. Check for broken or loose wires. 
4. Humidifier does not operate in auto mode.Check that the outdoor sensor is in order and operational. The outdoor temperature will be displayed on the screen if the outdoor sensor works. 
5. Display is blank, or Display flashes, or ‘LO BAT’ is on. This indicates that the batteries need to be changed. 
6. Incorrect time display.   To change the time, press the ‘P’ button followed by the up or down arrows, and once the correct time is displayed, press the ‘P’ button
7. Thermostat turns on, and off too often.The default setting is for the thermostat to activate if the temperature changes by one degree. You can adjust the programming to activate the thermostat once the temperature changes by two degrees.
8. Thermostat does not Follow the Program Schedule.Here you will have to go through four possible solutions. The thermostat is in manual mode and needs to be switched to program mode. To do this, press the ‘P’ button until the PROG position displays. Check that the thermostat is not programmed in the ‘heat’ or ‘cool’ position. Check that the programming times are correct. Make sure you have corrected for ‘am’ and ‘pm’. Check that the program day is correct. Remember, Monday is given as 1, Tuesday as 2, and so on. 
9. No Heat or No fanCheck that the switch is on. Check that the door panel has been correctly closed. Check that the wiring is secured and that no wires are touching. Ensure the power supply has been disconnected before checking the wires to avoid injury. 

Thermostat model 8263 troubleshooting guide

ProblemSolution
1. Unit does not switch on.Check that the unit has a power supply. Check the fuse and replace it if broken. A 3 Amp fuse is required. Make sure that the door panel has been correctly replaced. 
2. No HeatCheck that the thermostat wiring is complete and secure. Check that no wires are touching. You can check the system by switching the system to ‘Heat’ and raising the room temperature. This should result in the thermostat making a soft click which indicates the thermostat is working correctly. If there is no click from the thermostat, press the reset button. This restores the default setting. To reset, press the up and down arrows together with the TIME button. 
3. No CoolingThe process is similar to the heating sequence above, except now you will need to set the thermostat a few degrees cooler, and the thermostat should click in within 5 minutes. 
4. Fan runs continuouslyThis could result from a short in the wiring or the thermostat. Check for any loose or touching wires. Reset the thermostat using the sequence described in 2. above. 
5. Blank Screen.Usually, this results from a power spike. Resetting the system normally corrects the situation. (See two above)
6. Incorrect timeThe clock has suffered a break in the power supply. While the thermostat will maintain the program, the clock must be reset.

Thermostat model 8244 troubleshooting guide

ProblemSolution
1. Unit does not switch on.Check that the unit has a power supply. Check the fuse and replace it if broken. A 3 Amp fuse is required. Make sure that the door panel has been correctly replaced. 
2. No HeatCheck that the thermostat wiring is complete and secure. Check that no wires are touching. You can check the system by switching the system to ‘Heat’ and raising the room temperature. This should result in the thermostat making a soft click which indicates the thermostat is working correctly. If there is no click from the thermostat, press the reset button. This restores the default setting. To reset, press the up and down arrows together with the TIME button. 
3. No CoolingThe process is similar to the heating sequence above, except now you will need to set the thermostat a few degrees cooler, and the thermostat should click in within 5 minutes. 
4. Fan runs continuouslyThis could result from a short in the wiring or the thermostat. Check for any loose or touching wires. Reset the thermostat using the sequence described in 2. above. 
5. Thermostat and thermometer don’t show the same temperature.Check item 5 in the configuration menu section to adjust the thermometer by up to four degrees.
6. Blank Screen.Usually, this results from a power spike. Resetting the system normally corrects the situation. (See two above) 

Thermostat 8444, 8463 troubleshooting guide

The 8444 model is nonprogrammable, while the 8463 model does have programable functions.          

ProblemSolution
1. Unit does not switch on.Check that the unit has a power supply. Check the fuse and replace it if broken. A 3 Amp fuse is required. Make sure that the door panel has been correctly replaced. 
2. Display is blank, or Display flashes or ‘LO BAT’ is on. This indicates that the batteries need to be changed. 
3. Temperature settings do not change.Ensure your heating and cooling temperatures are set to the correct ranges. The right heat range is between 45 and 90 degrees F, and the cooling range is between 50 and 99 degrees F. If the settings are correct, check the 24VAC between the common and the power on the secondary side of the transformer. 
4. ‘Heating’ appears on the screen, but the system does not respond.Check the 24 VAC between the heat terminal and the transformer. If there is voltage present, the thermostat is operational. Check for broken or loose wires. If there is no voltage on the secondary side of the transformer, you will need to check the cooling equipment. 
5. ‘Cooling’ appears on the screen, but the system does not respond. Check that all the wires are securely fastened and that none are touching. If there is 24 VAC between the cooling terminal and the common thermostat, then you will have to check the cooling system. 
6. Heating and cooling are on at the same time.Check that there is no touching of the heating and cooling wires. 
7. Cooling is not displayed.Set the system to ‘cool’ mode and the temperature below the room temperature. 

Thermostat 8336 troubleshooting guide.

ProblemSolution
The display on the thermostat is blank.         Make sure the power supply is correct. Check that the switches to the heating and cooling systems are on. Check the circuit breaker or fuse. 
The thermostat shows a very highCheck the furnace door is properly closed. If there is a remote sensor connected, check that the dip switch is correctly set. 
The outdoor temperature does not appear on the screen.Check that the outdoor sensor has been correctly set up and the support module is set.

Support module 8081 TT troubleshooting guide

ProblemSolution
The display on the thermostat is blank.         Make sure the power supply is correct. Check that the switches to the heating and cooling systems are on. Check the circuit breaker or fuse. 
The outdoor temperature does not appear on the screen.Check that the outdoor sensor has been correctly set up and the support module is set.
The thermostat shows a very highCheck the furnace door is properly closed. If there is a remote sensor connected, check that the dip switch is correctly set. The dip switch must be set to read the remote sensor. 

Conclusion

Aprilaire Thermostats are super friendly to use, and the manuals provide extensive detail both on how to install the thermostat and to resolve issues if the unit malfunctions. By carefully reading through the manual, you will be able to resolve most of the issues around your thermostat, but if there is any doubt, please consult the Aprilaire Help desk.

FAQs

How to reset Aprilaire Thermostat?

Resetting your Aprilaire Thermostat is easy. Simply open the battery cover, and you will find the Reset button. Press the button to reset your Thermostat.

Why Aprilaire Thermostat Cooling Blinking?

The cool function blinking indicates that the thermostat is in delay mode, which can last up to five minutes. Once the five minutes are up, the flashing should stop. If, however, the flashing continues, then it indicates that the exterior component has been locked out of the system. You will need to check and make sure that the external component has been correctly connected to the unit.

How to unlock an Aprilaire Thermostat.

You can override this feature by pressing and holding the Menu button for seven seconds.

What does the Red light indicate on the Thermostat?

The red light indicates that the outdoor unit is not working.

What does a blinking red light on the furnace side indicate?

This indicates a possible dirty gas or limited air supply creating an unsteady flame.