Aprilaire Thermostat Troubleshooting

The tables below are Aprilaire Thermostat troubleshooting instructions – each for a different thermostat model.  Some of the tables allow identifying possible causes of malfunctions and fixing the issues. Each manual describes the Aprilaire Thermostat troubleshooting process in detail, starting from WiFi set up and finishing by heat option control.

Aprilaire 8336 Thermostat Troubleshooting

SymptomRemedy
Thermostat does not turn on system.Check Wiring
Check fuse. Replace with 2 amp fuse if fuse has opened.
Thermostat turns on and off too frequently.Increase Temperature Differential
System fan does not operate properly.Move fan option switch to either gas or electric, to match system
Thermostat does not display proper room temperature.Check "F" Fahrenheit "C" Celsius switch located at top center of the circuit board for proper position. If a new selection is made, press "RESET" button located directly below LCD display.

Aprilaire 8081TT Thermostat Troubleshooting

SymptomRemedy
THE THERMOSTAT 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
THE THERMOSTAT DISPLAYS A VERY HIGH TEMPERATUREVerify the appropriate setting of dip switch 6. If the dip switch is set to use the on board sensor, but a remote sensor is attached to T1&T2 then the temperature will read too high
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 8244 Thermostat Troubleshooting

SymptomPossible CauseCorrective Action
No Heat/No Cool/No Fan (common problems)1. Blown fuse or tripped circuit breaker.1. Replace fuse or reset breaker.
2. Furnace power switch to OFF.2. Turn switch to ON.
3. Furnace blower compartment door or panel loose or not properly installed.3. Replace door panel in proper position to engage 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 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 on, contact your heating and cooling service person or place of purchase for a replacement.
If the thermostat clicks, contact the furnace manufacturer or a sen/ice 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 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. 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, 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 DisagreeThermostat thermometer setting requires adjustment.The thermometer can be adjusted +/- 4 degrees. t
Blank Display and/or Keypad Not Responding1. Thermostat loss of power.1. Check possible blown fuse or tripped breaker.
2. Voltage spike or static discharge.2. Turn system power off. Wait for 5 minutes and turn the power on.

Aprilaire 8355 Thermostat Troubleshooting

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

Aprilaire Thermostat 8463, 8444 Troubleshooting

Problem Solution
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)
HEATING SYSTEM DOES NOT RESPOND ("HEATING” APPEARS ON 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
COOLING SYSTEM DOES NOT RESPOND ("COOLING" APPEARS ON 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