Aprilaire Thermostat Troubleshooting

Is your Aprilaire thermostat not working as it should? Is it flashing error codes or just not functioning as expected? This brief troubleshooting guide for various Aprilaire thermostat will assist you in determining the problem with your device and resolving it as soon as possible.

Aprilaire Thermostat Troubleshooting

How to Program  Aprilaire Thermostat

Before programming your programmable Aprilaire thermostat, you first have to set the time since it needs the clock to implement the different timed settings you will program into it.

1- Pressing the program button is the first step. This gives you the ability to change the time settings.
2- Normally, the AM/PM flashes, and you pick the proper one with the Up and Down buttons before pressing the mode button.

3- Proceed to the Hour, which is currently blinking, and adjust it with the up and down buttons. By pressing mode, you may save your changes. Using the same process, adjust the minutes and save the adjustment as you did before. If no additional buttons are pressed, the thermostat will display Done.

Here Are List of Aprilaire Thermostat Troubleshooting

Aprilaire 8244 Thermostat Troubleshooting Guide

ProblemCauseWhat to Do
No Heat/No Cool/No Fan (common problems)1. Blown fuse or tripped circuit breaker.
2. Furnace power switch to OFF.
3. Furnace blower compartment door or panel lose or not properly installed.
1. Replace fuse or reset circuit breaker.
2. Turn the switch to ON.
3. Replace the door panel in the proper position to engage safety interlock or door switch.
No Heat1. Pilot light not lit.
2. System Switch not set to HEAT.
3. Loose connection to thermostat or system.
4. Furnace Lock-Out Condition. Heat may also be intermittent.
5. Heating system requires service or the thermostat requires replacement.
1. Re-light pilot.
2. Set System Switch to HEAT and raise setpoint above room temperature.
3. Verify thermostat and system wires are securely attached.
4. Many furnaces have safety devices that shut down when a lock-out condition occurs. If the heat works intermittently, contact the furnace manufacturer or local service person for assistance.
Set System Switch to HEAT and raise the setpoint above room temperature. A soft click sound should be heard on the thermostat after a few seconds. If the thermostat does not click on, contact your heating and cooling service person or place of purchase for a replacement.
No Cool1. System Switch not set to COOL.
2. Loose connection to thermostat or system.
3. Cooling system requires service or thermostat requires replacement.
1. Set System Switch to COOL and lower setpoint below room temperature.
2. Verify thermostat and system wires are securely attached.
3. Same procedure as diagnostic for No Heat condition except set the thermostat to COOL and lower the setpoint below the room temperature. Wait for the click for up to 5 minutes.
Heat, Cool or Fan Runs Constantly1. Possible short in the wiring.
2. Possible short in thermostat.
3. Possible short in heat/cool/fan system.
4. Fan Switch set to Fan On.
Check each wire connection to verify they are not shorted or touching together. No bare wire should stick out from under terminal screws. If the condition persists, the manufacturer of your system or service person can instruct you on how to test the Heat/Cool system for correct operation. If the system operates correctly, replace the thermostat.
Furnace Cycles Too Fast or Too Slow (narrow or wide temperature swing)The location of the thermostat and/or the size of the Heating System may be influencing the cycle rate.Digital thermostats normally provide precise temperature control and may cycle faster than some older mechanical models. A faster cycle rate means the unit turns on and off more frequently but runs for a shorter time so there is no increase in energy use. If you would like to increase the cycle time, go to menu mode as mentioned in the instructions for Hydronic Heating Systems. It is not possible to shorten the cycle time. If an acceptable cycle rate is not achieved as received or by changing cycle time from FAST to SLOW on the menu mode, contact a local service person for additional suggestions.
Cooling Cycles Too Fast or Too Slow (narrow or wide temperature swing)The location of the thermostat and/or the size of the Cooling System can influence the cycle rate.The cycle rate for cooling is fixed and cannot be adjusted. Contact a local service person for suggestions.
Thermostat Setting and Thermostat Thermometer DisagreeThe thermostat thermometer setting requires adjustment.The thermometer can be adjusted +/- 4 degrees. t
Blank Display and/or Keypad Not Responding1. Thermostat loss of power.
2. Voltage spike or static discharge.
1. Check the possible blown fuse or tripped breaker.
2. Turn the system power off. Wait for 5 minutes and turn the power on.

Aprilaire 8263 thermostat troubleshooting

SymptomPossible CauseWhat to Do
No Heat/No Cool/No Fan (common problems)1. Blown fuse or tripped circuit breaker.1. Replace the fuse or reset the breaker.
2. Furnace power switch to OFF.2. Turn the switch to ON.
3. Furnace blower compartment door or panel lose or not properly installed.3. Replace the door panel in the proper position to engage the safety interlock or door switch.
No Heat1. Pilot light not lit.1. Re-light pilot.
2. System Switch not set to HEAT.2. Set System Switch to HEAT and raise setpoint above room temperature.
3. Loose connection to thermostat or system.3. Verify thermostat and system wires are securely attached.
4. Furnace Lock-Out Condition. Heat may also be intermittent.4. Many furnaces have safety devices that shut down when a lock-out condition occurs. If the heat works intermittently, contact the furnace manufacturer or local service person for assistance.
5. Heating system requires service or the thermostat requires replacement.5. Diagnostic: Set System Switch to HEAT and raise the setpoint above room temperature. Within a few seconds, the thermostat should make a soft click sound. This sound usually indicates the thermostat is operating properly. If the thermostat does not click, try the reset operation listed above. If the thermostat does not click after being reset contact your heating and cooling service person or place of purchase for a replacement. If the thermostat clicks, contact the furnace manufacturer or a service person to verify the heating is operating correctly.
No Cool1. System Switch not set to COOL.1. Set System Switch to COOL and lower setpoint below room temperature.
2. Loose connection to thermostat or system.2. Verify thermostat and system wires are securely attached.
3. Cooling system requires service or thermostat requires replacement.3. Same procedure as diagnostic for No Heat condition except set the thermostat to COOL and lower the setpoint below the room temperature. There may be up to a five-minute delay before the thermostat clicks in Cooling.
Heat, Cool, or Fan Runs Constantly1. Possible short in the wiring.1.-4. Check each wire connection to verify they are not shorted or touching together. No bare wire should stick out from under terminal screws. Try resetting the thermostat as described. If the condition persists, the manufacturer of your system or service person can instruct you on how to test the Heat/Cool system for correct operation. If the system operates correctly, replace the thermostat.
2. Possible short in thermostat.
3. Possible short in heat/cool/fan system.
4. Fan Switch set to Fan On.
Furnace Cycles Too Fast or Too Slow (narrow or wide temperature swing)The location of the thermostat and/or the size of the Heating System may be influencing the cycle rate.Digital thermostats normally provide precise temperature control and may cycle faster than some older mechanical models. A faster cycle rate means the unit turns on and off more frequently but runs for a shorter time so there is no increase in energy use. If you would like to increase the cycle time, change the cycle rate to “SL“ in the configuration menu. It is not possible to shorten the cycle time. If an acceptable cycle rate is not achieved as received or by changing the cycle rate, contact a local service person for additional suggestions.
Cooling Cycles Too Fast or Too Slow (narrow or wide temperature swing)The location of the thermostat and/or the size of the Cooling System can influence the cycle rate.The cycle rate for cooling is fixed and cannot be adjusted. Contact a local service person for suggestions.
Thermostat Setting and Thermostat Thermometer DisagreeThe thermostat thermometer setting requires adjustment.The thermometer can be adjusted +/- 4 degrees.
Thermostat Does Not Follow Program1. AM or PM set incorrectly in the program.1.-3. Check the current clock and program settings including the AM or PM designations for each time period. If a voltage spike or a static discharge occurs use the Reset Operation
2. AM or PM set incorrectly on the clock.
3. Voltage spike or static discharge.
4. Thermostat may be performing Progressive Recovery actions.4. Disable Progressive Recovery from the Configuration Menu if this feature is not desired.
Blank Display and/or Keypad Not RespondingVoltage spike or static discharge.If a voltage spike occurs, use the Reset Operation
Clock Loses or Gains TimeLoss of power to the thermostat.The thermostat will maintain its program in memory even with no power but the clock time will be incorrect when power is restored.
Heat or Cool Starts EarlyProgressive Recovery activated.

Aprilaire Thermostat 8463, 8444  Troubleshooting

ProblemWhat to Do
DISPLAY IS BLANK• Check circuit breaker and reset if necessary.
• Make sure power switch at heating & cooling system is on.
• Make sure furnace door is closed securely.
• If thermostat is battery powered, make sure fresh AA alkaline batteries are correctly installed
TEMPERATURE SETTINGS DO NOT CHANGEMake sure heating and cooling temperatures are set to acceptable ranges: • Heat: 45° to 90°F (7° to 32°C). • Cool: 50° to 99°F (10° to 37°C)
THE HEATING SYSTEM DOES NOT RESPOND (“HEATING” APPEARS ON THE SCREEN)• Check for 24 VAC at the equipment on the secondary side of the transformer between power and common. If voltage is not present, check the heating equipment to find the cause of the problem.
• Check for 24 VAC between the heat terminal (W) and the transformer common. If 24 VAC is present, the thermostat is functional. Check the heating equipment to find the cause of the problem.
• Check for loose or broken wires between the thermostat and the heating equipment
THE COOLING SYSTEM DOES NOT RESPOND (“COOLING” APPEARS ON THE SCREEN)• Check for 24 VAC at the equipment on the secondary side of the transformer between power and common. If voltage is not present, check the cooling equipment to find the cause of the problem.
• Check for 24 VAC between the cooling terminal (Y) and the transformer common. If 24 VAC is present, the thermostat is functional. Check the cooling system to find the cause of the problem.
• Check for loose or broken wires between the thermostat and the cooling equipment
FAN DOES NOT TURN ON IN A CALL FOR HEAT• Check System Setting #02 (Fan Control), to make sure the fan control is properly set to match the type of system
HEAT PUMP ISSUES COOL AIR IN HEAT MODE, OR WARM AIR IN COOL MODE• Check System Setting #12 (Reversing Valve), to make sure it is properly configured for your system
HEAT/COOL BOTH ON AT SAME TIME• Check SW1 (Equipment Type), to make sure it is set to match the installed heating/cooling equipment
• Check to make sure heating and cooling wires are not shorted together
HEATING EQUIPMENT IS RUNNING IN COOL MODE• Check SW1 (Equipment Type), to make sure it is set to match the installed heating/cooling equipment
“HEATING” IS NOT DISPLAYED• Change the System Mode to Heat, and set the temperature level above the current room temperature
“COOLING” IS NOT DISPLAYED• Change the System Mode to Cool, and set the temperature level below the current room temperature

Aprilaire 8620 thermostat troubleshooting

ProblemCause/What to Do
DISPLAY IS BLANK• Check the circuit breaker and reset if necessary.
• Make sure the power switch at the heating & cooling system is on.
• Make sure the furnace door is closed securely.
• If the thermostat is battery powered, make sure fresh AA alkaline batteries are correctly installed.

TEMPERATURE SETTINGS DO NOT CHANGEMake sure heating and cooling temperatures are set to acceptable ranges:
• Heat: 40° to 90°F (4° to32°C).
• Cool: 50° to 99°F|10° to37°C).

THE HEATING SYSTEM DOES NOT RESPOND (“HEATING” APPEARS ON THE SCREEN)• Check for 24VAC at the equipment on the secondary side of the transformer between power and common. If voltage is not present, check the heating equipment to find the cause of the problem.
• Check for 24VAC between the heat terminal (W| and the transformer common. If 24VAC is present, the thermostat is functional. Check the heating equipment to find the cause of the problem.
• Check for loose or broken wires between the thermostat and the heating equipment.
THE COOLING SYSTEM DOES NOT RESPOND (“COOLING” APPEARS ON THE SCREEN)• Check for 24VAC at the equipment on the secondary side of the transformer between power and common. If voltage is not present, check the cooling equipment to find the cause of the problem
• Check for 24VAC between the cooling terminal (Y) and the transformer common. If 24VAC is present, the thermostat is functional. Check the cooling system to find the cause of the problem.
• Check for loose or broken wires between the thermostat and the cooling equipment.
FAN DOES NOT TURN ON IN A CALL FOR HEAT• Check System Setting 05 (Fan Control), to make sure the fan control is properly set to match the type of system
HEAT PUMP ISSUES COOL AIR IN HEAT MODE. OR WARM AIR IN COOL MODE• Check System Setting 31 (O/B Operation) to make sure the reversing valve operation matches the heat pump.
HEAT/COOL BOTH ON AT THE SAME TIME• Check SW1 (Equipment Type), to make sure it is set to match the installed heating/cooling equipment
• Check to make sure heating and cooling wires are not shorted together.
HEATING EQUIPMENT IS RUNNING IN COOL MODE• Check SW1 (Equipment Type), to make sure it is set to match the installed heating/cooling equipment
“HEATING” IS NOT DISPLAYED• Check Installer System Setting number 01 (Control Setup) is set correctly.
• Change the System Mode to Heat, and set the temperature level above the current room temperature.
“COOLING” IS NOT DISPLAYED• Check Installer System Setting number 01 (Control Setup) is set correctly.
• Change the System Mode to Cool, and set the temperature level below the current room temperature.
HUMIDIFIER DOES NOT OPERATE IN AUTO MODE• Check Installer System Setting number 11 (Outdoor Sensor) is set to yes.
• Verify that the outdoor sensor is functioning correctly. If the sensor is functioning correctly the outdoor temperature will display in the outdoor temperature location

Aprilaire 8355 thermostat troubleshooting

SymptomWhat to Do
The thermostat does not turn on the system.Check Wiring
Check fuse. Replace with 3 amp fuse if the fuse has opened. Five-minute compressor short cycle protection may be in effect. Press RESET to override. NOTE: This will erase programming.
The thermostat turns on and off too frequently.Increase Temperature Differential
The display is blank, flashing or constant “LO BAT.”Replace batteries.
The time shown on display is not the current time of day.Change time of day setting
The thermostat does not follow the program.The thermostat in MANUAL mode
The thermostat may not have been programmed in HEAT or COOL position. Verify program.
Check AM/PM indicators at the time of day and programmed time changes
Verify program and day of the week is correct
The thermostat does not advance the day of the week.To view or change the day of the week use the method

Aprilaire 8336 Thermostat Troubleshooting

SymptomWhat to Do
THE THERMOSTAT DISPLAY IS BLANK• Check circuit breaker and reset if necessary.
• Make sure the power switch at the heating & cooling system is on.
• Make sure furnace door is closed securely
THE THERMOSTAT DISPLAYS A VERY HIGH TEMPERATUREVerify the appropriate setting of dip switch 6. If the dip switch is set to use the onboard sensor, but a remote sensor is attached to T1&T2 then the temperature will read too high
THE THERMOSTAT DOES NOT DISPLAY THE OUTDOOR TEMPERATURE FROM THE SUPPORT MODULE• Verify that the does not have an outdoor temperature sensor already attached and enabled.
• Verify that the support module is set

Aprilaire 8081TT Thermostat Troubleshooting

SymptomWhat to Do
THE THERMOSTAT DISPLAY IS BLANK• Check the circuit breaker and reset if necessary.
• Make sure the power switch at the heating & cooling system is on.
• Make sure furnace door is closed securely
THE THERMOSTAT DISPLAYS A VERY HIGH TEMPERATUREVerify the appropriate setting of dip switch 6. If the dip switch is set to use the onboard sensor, but a remote sensor is attached to T1&T2 then the temperature will read too high
THE THERMOSTAT DOES NOT DISPLAY THE OUTDOOR TEMPERATURE FROM THE SUPPORT MODULE• Verify that the does not have an outdoor temperature sensor already attached and enabled.
• Verify that the support module is set

Frequently Asked Question       

Aprilaire thermostat cooling blinking

If your thermostat continues to flash during regular AC operation, it’s likely that there’s a problem with the system’s exterior component. It’s effectively been locked out, which means it’s turned off and sent a signal to the thermostat alerting it to a problem.

How to reset Aprilaire thermostat

The reset button located under the battery cover can be used to reset the thermostat back to factory defaults. Seconds to reset a service reminder message. 2. Press or to adjust the hour.

How To Unlock Aprilaire Thermostat

This feature can be overridden by pressing and holding [MENU] for 7 seconds

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