Lennox thermostats troubleshooting

The advanced developments of the Lennox company affect equipment, inter alia, thermostats, as well as systems for their maintenance. In particular, the table of Lennox thermostats troubleshooting is presented below. Everything for service of consumers!

If...Then ...
Key to the right of the screen key is blank.MORE key remains blank unless the Furnace Filter Change Reminder has been turned on. See User Set-Up Number 0500.
Display is blank.Check that fresh AAA alkaline batteries are installed as marked on the thermostat.
Temperature settings do not change.Check that temperature settings are:
• Heating 40°F to 90°F (4.5°C to 32°C).
• Cooling 50°F to 99°F (10°C to 37°C).
Heating system does not turn on.• Set the system to heat by pressing the SYSTEM key.
• Check the heat temperature setting to be sure it is set above the room temperature and "Heat On” is displayed solidly on the screen.
• Check the circuit breaker to make sure it is not tripped.
• Check the power switch at the heating and/or cooling system to make sure it is on.
• Check the furnace door to make sure it is closed securely.
• Wait five minutes for the heating system to respond.
• If the problem has not been identified and corrected, contact a qualified service technician.
Cooling system does not turn on.• Set the system to Cool by pressing the SYSTEM key.
• Check the cool temperature setting to be sure it is set below the room temperature and "Cool On” is displayed solidly on the screen.
• Check the circuit breaker to make sure it is not tripped.
• Check the power switch at the heating and/or cooling system to make sure it is on.
• Check the furnace door to make sure it is closed securely.
• Wait five minutes for the cooling system to respond.
• If the problem has not been identified and corrected, contact a qualified service technician.
Cannot set System setting to Cool.Check Installer Set-Up Number 170: Heating and/or Cooling Type*. Make sure the setting matches the installed heating and/or cooling system.
’’Heat On” is not displayed on the screen.Set the System setting to Heat and set the temperature setting above the room temperature. If “Heat On” is shown solidly in the display, but the heating system does not turn on
’’Cool On” is not displayed on the screen.Set the System setting to Cool and set the temperature setting below the room temperature. If “Cool On” is shown solidly in the display, but the cooling system does not turn on
“Wait” is displayed on the screen.Compressor minimum-off timer is activated. Wait up to five minutes for the compressor to turn on.
Fan does not turn on in a call for heat (electric furnaces only)Check Installer Set-Up 0180: Fan Control in Heating*. Make sure Electric Heat option is selected.
Both heating and cooling systems are operating at the same time.Check Installer Set-Up Number 170: Heating and/or Cooling Type*. Make sure the setting matches the installed heating and/or cooling system. Check to ensure that bare portions of wires are not touching.
Heating is running in Cool mode.Check Installer Set-Up Number 170: Heating and/or Cooling Type*. Make sure the setting matches the installed heating and/or cooling system.
Heating system does not turn off and the heat temperature setting is set below the room temperature (’’Heat On” is not shown in display.)Check Installer Set-Up Number 170: Heating and/or Cooling Type*. Make sure the setting matches the installed heating and/or cooling system.
Red LED is lit in the upper right corner of the thermostat when the system monitor detects a possible problem.A system monitor is wired to the thermostat L terminal. Refer to suggestions given in Heating or Cooling System Does Not Turn On sections in this table.

Lennox icomfort Wi-Fi thermostat troubleshooting

Alert CodePriorityAlert TextSteps to clear
10Critical(Stat) The thermostat has found an unknown device on the system.An unknown device is seen on the subnet in or outside of configuration mode. Clear by reconfiguring the system. Press the setup tab, press start, and press confirm. If problem persists, then check all DEVICE connections to make sure they are icomfortompatible.
11Critical(Stat) The thermostat cannot find a previously installed unit.Check all connections and cycle system power. If problem persists, clear by reconfiguring the sys- tem. Press the setup tab, press start, and press confirm. If problem persists, then check all DEVICE connections to make sure they are icomfort-compatible.
12Critical(Stat) The thermostat cannot find an icomfortenabled indoor unit.Thermostat did not find an Indoor Unit. Make sure there is an icomfort indoor unit on the system. Check R, i+, i- and C connections, ohm wires and cycle power. Replace indoor unit control board if there is no response.
14Critical(Stat) The thermostat found more than one thermostat, more than one indoor unit, or more than one outdoor unit on the system.Check wiring and remove duplicate equipment. Reconfigure system.
18Minor(Stat) The outside temperature is below the level where the heat pump is programmed to heat the home. The system will not use the heat pump to warm your home.Notification only - Outdoor Temp is below the Low Balance Point. Heat Pump will not be used to service a heating demand.
19Minor(Stat) The outside temperature is higher than the level where the furnace or electric heat is programmed to work. The system will only use the heat pump to warm your home.Notification only - Outdoor Temp is above the High Balance Point. Indoor Unit (furnace or air-handier) will not be used to service a heating demand.
29Critical(Stat) The thermostat is reading an indoor temperature that is higher than 99?F. The thermo- stat will not allow any heating operation to begin until it senses a temperature lower than 99?F.Indoor temperature rose above 99?F during a heating or cooling demand. Heating operation is not allowed. Check to ensure that Heating Equipment is not stuck ON (reversing valve, etc.). Check the accuracy of the thermostat temperature sensor. Select cooling system mode to cool the indoor space.
30Moderate(Stat) The thermostat is reading an indoor temperature that is lower than 40?F. The thermostat will not allow any cooling operation to begin until it senses a temperature higher than 40?F.Indoor Temp fell below 40?F. Cooling operation is not allowed. Check to ensure that cooling equipment is not stuck ON. Check accuracy of the thermostat temperature sensor. Select heating system mode to heat the indoor space to above 40?F.
31Critical(Stat) The thermostat has lost communication with the (furnace, air-handier or outdoor unit) for more than 3 minutes.[Indicated uni? has not communicated with thermostat for more than 3 minutes. Check connections. Ohm wires. If fault persists, then cycle power. Fault clears after communication is restored.
32Moderate(Stat) The (furnace, air-handier or outdoor unit) is resetting itself.[Indicated unif\ is resetting itself. This event may occur during a power outage or power fluctuation in the system. If persistent or if it coincides with the system operation then proceed with the following steps. Check the power connections, check the amp draw at the transformer (the transformer maybe overloaded) and check 24VAC voltage at the DEVICE. The alarm is only cleared by pressing the clear button on the Installer Alerts Tab. If the fault persists after checking the connections, replace the unit’s control board.
34Critical(Stat) The thermostat does not know the capacity (tonnage) of the (furnace, air-handier or out- door unit). Please program the correct capacity of the (furnace, air-handier or outdoor unit).[Indicated unif\ is missing the programmed unit capacity. Go to [Indicated unif\ and program the unit capacity manually. See the unit IOM for programming instructions. Remove power to thermostat before programming the unit control board. Once programming is complete, reconnect thermostat wires and reconfigure system.
36Critical(Stat) The system has been heating for at least 15 minutes, without a demand for heating.Run the system in diagnostic mode and verify that it matches actual equipment operation. Check for other alarms/codes that may be preventing the system from operating as expected.
Step 1: Check all heating equipment to determine cause of heating demand.
Step 2: Recycle power.
System will clear code when it detects condition has cleared.
37Critical(Stat) The system has been cooling for at least 15 minutes, without a demand for cooling.Run the system in diagnostic mode and verify that it matches actual equipment operation. Check for other alarms/codes that may be preventing the system from operating as expected.
Step 1: Check all cooling equipment to determine cause of cooling demand.
Step 2: Recycle power.
System will clear code when it detects condition has cleared.
38Critical(Stat) The system has not been able to turn on the heating for more than 45 minutes. The sys- tem will go offline for 60 minutes and try again.Run the system in diagnostic mode and verify that it matches actual equipment operation. Check for other alarms/codes that may be preventing the system from operating as expected.
Step 1: Check all heating equipment to determine cause.
Step 2: Recycle power.
System will clear code when it detects condition has cleared.
39Critical(Stat) The system has not been able to turn on the cooling for more than 45 minutes. The sys- tem will go offline for 60 minutes and try again.Run the system in diagnostic mode and verify that it matches actual equipment operation. Check for other alarms/codes that may be preventing the system from operating as expected.
Step 1: Check all cooling equipment to determine cause.
Step 2: Recycle power.
System will clear code when it detects condition has cleared.
105Critical(Stat / Furnace / Air Handler / Outdoor Unit) The (stat, furnace, air-handier or outdoor unit) has lost communication with the rest of the system.Equipment is unable to communicate. This may indicate the existence of other alarms/codes. In most cases errors are related to electrical noise. Make sure high voltage power is separated from RSBus. Check for miswired and/or loose connections between the stat, indoor unit and outdoor unit. Check for a high voltage source of noise close to the system. Generally, this is a self-recoverable error.
110Critical(Furnace) The line voltage is too low.This alarm/code may appear during a brownout. Line voltage is below its designed operating value. Check and correct the power line voltage.
111Critical(Furnace) The line power voltage wiring is re- versed.The unit is reporting that its power line and neutral are reversed. Turn off the power to the system and correct the line power voltage wiring. System resumes normal operation 5 seconds after fault recovered.
112Critical(Furnace) The reporting device cannot find earth ground. The thermostat will shut down the system.Provide proper earth ground to the equipment. System resumes normal operation 5 seconds after fault recovered.
System resumes normal operation 5 seconds after fault recovered.
114Critical(Furnace / Air Handler) There is a frequency/ distortion problem with the power to the (furnace or air-handier).This alarm/code may indicate transformer overloading. Check the voltage and line power frequency. Check the generator operating frequency, if the system is running on back-up power. Correct voltage and frequency problems. System resumes normal operation 5 seconds after fault recovered.
115Critical(Furnace / Air Handler) The 24VAC to the (furnace or air-handier control board) is lower than the required range of 18 to 30VAC.24-Volt Power Low (Range is 18 to 30 volts). Check and correct voltage. Check for additional power- robbing equipment connected to system. This alarm/code may require the installation of an addition- al or larger VA transformer.
117Minor(Furnace) The reporting unit has poor earth grounding.Provide proper grounding for the unit. Check for proper earth ground to the system. The alarm/code will clear 30 seconds after it is corrected.
120Moderate(Stat / Furnace / Air Handler / Outdoor Unit) There is a delay in the (stat, furnace, air-handier or outdoor unit) responding to the system.Typically, this alarm/code does not cause any issues and will clear on its own. The alarm/code is usually caused by a delay in the outdoor unit responding to the thermostat. Check all wiring connections. Cleared after unresponsive device responds to any inquiry.
124Critical(Stat / Furnace / Air Handler / Outdoor Unit) The thermostat has lost communication with the (furnace, air-handier or outdoor unit) for more than 3 minutes.Equipment lost communication with the thermostat. Check the wiring connections, ohm wires and cycle power. The alarm stops all associated HVAC operations and waits for a heartbeat message from the unit that’s not communicating. The alarm/fault clears after communication is re-established.
125Critical(Stat / Furnace / Outdoor Unit) There is a hard- ware problem on either the (stat, furnace control board, air-handier control board or outdoor unit control board).There is a control hardware problem. Replace the control if the problem prevents operation and is persistent. The alarm/fault is cleared 300 seconds after the fault recovers.
126Critical(Furnace / Outdoor Unit) There is an internal communication problem with the (furnace control board, air-handier control board or outdoor unit control board).There is an internal hardware problem on the control. Typically the control will re-set itself. Replace the control if the problem prevents operation and is persistent. The alarm/fault is cleared 300 seconds after the fault recovers.
130Moderate(Air Handler) An air-handier configuration jumper is missing.Configuration jumper(s) missing on control (applicable in non-communicating applications only). Replace the jumper or put wire between terminals on control. Cleared after jumper is connected.
131Critical(Stat / Furnace / Air Handler / Outdoor Unit) The (stat, furnace, air-handier or outdoor unit) control parameters are corrupted.Reconfigure the system. Replace the control if heating or cooling is not available.
132Critical(Air Handler) The air handler control software is corrupted.Recycle power. If failure re-occurs, replace the control. System reset is required to recover.
200Critical(Furnace) The furnace rollout limit switch is open.Correct the cause of rollout trip. Reset rollout switch. Reset power to clear. Test the furnace operation. The alarm/fault clears after the furnace rollout switch is closed.
201Critical(Furnace / Air Handler) The system has lost communication with the (furnace or air-handier) indoor blower motor.Lost communication with indoor blower motor. Possible causes include: power outage, brown-out, motor not powered, loose wiring, condensation on air handler control without cover on breaker. Problem may be on control or motor side. Cleared after communication is restored.
202Critical(Furnace / Air Handler) The unit size code for the (furnace or air-handier) and the size of blower motor do not match.Incorrect appliance unit size code selected. Check for proper configuring under Unit Size Codes for Furnace/Air Handler on configuration guide or in installation instructions. The alarm/fault clears after the correct match is detected following a reset. Remove the thermostat from the system while applying power and reprogramming.
203Critical(Furnace / Air Handler) The unit size code for the (furnace or air-handier) has not been selected.No appliance unit size code selected. Check for proper configuring under: Unit Size Codes for Furnace/Air Handler on configuration guide or in installation instructions. Critical Alert. The alarm/fault clears after the correct match is detected following a reset. Remove the thermostat from the system while applying power and reprogramming.
204Critical(Furnace) There is a problem with the furnace gas valve.Check gas valve operation and wiring. The alarm/fault clears after the issue is corrected.
205Critical(Furnace) The furnace gas valve relay contact is closed.Check wiring on control and gas valve. The alarm/fault clears after the issue is corrected.
206Critical(Furnace) The furnace gas valve 2nd stage relay is faulty.Furnace will operate on 1st stage for the remainder of the heating demand. The alarm/fault will clear after the issue is corrected. If unable to operate 2nd stage, replace control.
207Critical(Furnace) The furnace hot surface igniter is open.Measure the resistance of hot surface igniter. Replace the it if it is not within the specified range found in IOM. The alarm/fault clears after the issue is corrected.
223Critical(Furnace) The furnace low pressure switch is open.Check pressure (inches w.c.) of low pressure switch closing during a heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault clears after the issue is corrected.
224Critical(Furnace) The furnace low pressure switch is stuck closed.Check operation of low pressure switch to see if it is stuck closed for longer than 150 seconds during a heat call . Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault clears after the issue is corrected.
225Critical(Furnace) The furnace high pressure switch is failing to close.Check pressure (inches w.c.) of high pressure switch closing during a heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault clears after the issue is corrected.
226Critical(Furnace) The furnace high pressure switch is stuck closed.Check operation of high pressure switch closing during a heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault clears after the issue is corrected.
227Moderate(Furnace) The furnace low pressure switch is open in run mode.Check pressure (inches w.c.) of low pressure switch closing during a heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault clears after the issue is corrected.
228Moderate(Furnace) The furnace control is not able to cali- brate the pressure switch.Unable to perform pressure switch calibration. Check vent system and pressure switch wiring connections. Check the drain trap for blockage. The alarm/fault clears after a success- ful calibration.
229Minor(Furnace) The furnace control has switched to high fire ignition because the low fire pressure switch did not close in the allowed time.IFC switched to high fire ignition because low fire pressure switch did not close in allowed time. No action is needed.
240Moderate(Furnace) The furnace flame current is low.Check micro-amperes of the flame sensor using thermostat diagnostics. Clean or replace the flame sensor. Measure voltage of neutral to ground to ensure good unit ground. The alarm clears after a proper micro-amp reading has been sensed.
241Critical(Furnace) The furnace flame is going out while the furnace is heating.Shut off gas. Check for a gas valve leak. Replace the gas valve if needed. The alarm/fault will clear when a heat call ends successfully.
250Moderate(Furnace) The furnace primary limit switch is open.Check for proper firing rate on furnace. Ensure there is no blockage in the furnace and the ductwork. Check for proper air flow. If limit switch is not closed within 3 minutes, the unit will go into 1-hour Watchguard mode. The alarm/fault will clear when a heat call ends successfully.
252Moderate(Furnace) The furnace discharge air-tempera- ture is high.Check temperature rise, air flow and input rate. Check for dirty filters. The alarm/fault will clear when a heat call ends successfully.
270Critical(Furnace) The furnace is in Watchguard mode. The furnace igniter cannot turn on the flame.Check for proper gas flow. Ensure that igniter is lighting burner. Check flame sensor current. Check for dirty filters. The alarm/fault will clear on successful ignition.
271Critical(Furnace) The furnace is in Watchguard mode. The furnace low pressure switch is open.Check pressure (inches w.c.) of low pressure switch closing during a heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault will clear on successful ignition.
272Critical(Furnace) The furnace is in Watchguard mode. The furnace low pressure switch is open during run mode.Check operation of low pressure switch to see if it is stuck open during a heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. The alarm/fault will clear when a heat call ends successfully.
273Critical(Furnace) The furnace is in Watchguard mode. The furnace flame is going off during a heating cycle.Check micro-amperes of flame sensor using thermostat diagnostics. Clean or replace sensor. Mea- sure voltage of neutral to ground to ensure good unit ground. The alarm/fault will clear when a heat call ends successfully.
274Critical(Furnace) The furnace limit switch has been open for more than 3 minutes.The system will go into Watchguard mode. Check firing rate and air flow. Check for blockage. The alarm/fault will clear when a heat call ends successfully.
275Critical(Furnace) The furnace flame is out of sequence.The system will go into Watchguard mode. Shut off gas. Check for gas valve leak. The alarm/fault will clear on next successful ignition.
276Critical(Furnace) The furnace is not able to calibrate or the high pressure switch opened or failed to close in run mode.The system will go into Watchguard mode. Check vent system and pressure switch wiring connections. The fault/alarm will clear when the furnace calibrates itself successfully.
290Critical(Furnace) There is a problem with the furnace ignition circuit.The system will go into Watchguard mode. Measure resistance of hot surface igniter. Replace the hot surface ignitor it is not within specifications. The alarm/fault will clear on next successful ignition.
291Critical(Furnace) The heating airflow is below the mini- mum required level.The system will go into Watchguard mode. Check for dirty filters and other air flow restrictions. Check blower performance. The alarm/fault will clear when a heat call ends successfully.
292Critical(Furnace / Air Handler) The (furnace or air-han- dler) indoor blower motor will not start.The system will go into Watchguard mode. Indoor blower motor unable to start. This could be due to seized bearing, stuck wheel, obstruction etc. Replace motor or wheel if assembly does not operate or meet performance standards. The alarm/fault clears after the indoor blower motor starts successfully.
294Critical(Furnace) There is over current in the furnace inducer motor.The system will go into Watchguard mode. Check combustion blower bearings, wiring and amps. Replace if does not operate or does not meet performance standards. The alarm/fault clears after inducer current is sensed to be in-range after the ignition following the Watchguard mode or reset.
295Minor(Furnace) The indoor blower motor is over heat- ing.Indoor blower motor over temperature (motor tripped on internal protector). Check motor bearings and amps. Replace if necessary. The alarm/fault clears after blower demand is satisfied.
310Critical(Furnace / Air Handler) There is a problem with (furnace or air-handier) discharge air sensor.Compare outdoor sensor resistance to temperature/resistance charts in installation instructions. Replace sensor if necessary. The alarm/fault is cleared 30 seconds after fault is detected as recov- ered.
311Minor(Furnace) The heat firing rate has been reduced to match available airflow (cutback mode).Warning Only. Furnace blower in cutback mode due to restricted airflow. Reduce firing rate every 60 seconds to match available CFM. Check filter and duct system. To clear, replace filter if needed or repair/add duct. 2-stage controls will reduce firing rate to 1st stage. The alarm/fault clears when a heat call finishes successfully.
312Minor(Furnace / Air Handler) The blower cannot pro- vide the requested CFM due to high static.Warning Only. Restricted airflow - Indoor blower is running at a reduced CFM (Cutback Mode - The variable speed motor has pre-set speed and torque limiters to protect the motor from damage caused by operating outside of design parameters (0 to 0.8” e.g.. total external static pressure). Check filter and duct system. To clear, replace filter if needed or repair/add duct. The alarm/fault is cleared after the current service demand is satisfied.
313Minor(Furnace / Air Handler) The indoor and outdoor unit capacities do not match.Check for proper configuring in installation instructions. Alarm is just a warning. The system will operate, but might not meet efficiency and capacity parameters. The alarm will clear after commissioning is complete.
344Critical(Furnace) Relay Y1 FailureY1 relay failed; operation stopped. Alarm clears 300 seconds after Y1 input sensed OFF.
346Critical(Air Handler) The heat pump jumper was not removed on the air-handier control board.Configuration link(s) not removed on control. Cut O-R. Applicable with non communicating outdoor unit with communicating indoor system.
347Critical(Furnace / Air Handler) The “Y1” relay on the (furnace or air-handier) has failed. Either the pilot relay contacts did not close or the relay coil did not energize.Operation stopped. Y1 relay / Stage 1 failed. (Pilot relay contacts did not close or the relay coil did not energize; no input back to IFC chip). Critical Alert. Cleared after eset and Y1 input sensed.
348Critical(Furnace / Air Handler) The “Y2” relay on the (furnace or air-handier) has failed. Either the pilot relay contacts did not close or the relay coil did not energize.Y2 relay / Stage 2 failed. (Pilot relay contacts did not close or the relay coil did not energize; no input back to IFC chip). Critical Alert. Cleared after reset and Y1 input sensed.
349Critical(Furnace) The “0” to “R” jumper on the furnace needs to be restored.Configuration link R to 0 needs to be restored. Replace link or hard-wire. Applicable in non communicating mode. Critical Alert.
350Critical(Air Handler) The air-handler’s electric heat is not configured.Heat call with no configured or mis-configured electric heat. Check for proper configuring under Configuring Electric Heat Stages in the air handler installation instructions. Cleared after electrical heat detection is successful.
351Critical(Air Handler) There is a problem with the air- handler’s 1st stage electric heat. Either the pilot relay contacts did not lose, or the relay coil in the electric heat section did not energize.Heat section / Stage 1 failed. (Pilot relay contacts did not close, or the relay coil in the electric heat section did not energize.) Air handler will operate on 1st stage for reminder of the heat call. Will clear after fault recovered.
352Critical(Air Handler) There is a problem with the air- handler’s 2nd stage electric heat. Either the pi- lot relay contacts did not close, or the relay coil in the electric heat section did not energize. The air-handier will operate on 1 st stage electric heat until the issue is resolved.Heat section / Stage 2 failed (Same as Code 351).
354Critical(Air Handler) There is a problem with the air- handler’s 4th stage electric heat. Either the pilot relay contacts did not close, or the relay coil in the electric heat section did not energize. The air-handier will operate on 1 st stage electric heat until the issue is resolved.Heat section / Stage 4 failed (Same as Code 351).
355Critical(Air Handler) There is a problem with the air- handler’s 5th stage electric heat. Either the pilot relay contacts did not close, or the relay coil in the electric heat section did not energize. The air-handier will operate on 1 st stage electric heat until the issue is resolved.Heat section / Stage 5 failed (Same as Code 351).
370Critical(Furnace) The furnace control board has not received 24VAC power for 2 minutes or more.Control sees the loss of 24VAC for 2 minutes .Terminate all services and wait for interlock switch to close. The alarm will clear when 24VAC is continuously sensed on DS terminal for a minimum of 10 seconds or on a power reset. If 2 stage with float switch, the IFC control R-DS is open.
400Critical(Outdoor Unit) The compressor internal over- load has tripped.Thermostat demand Y1 is present; but, compressor is not running. Check power to unit. Clears the error after current is sensed in both RUN and START sensors for at least 2 seconds, or after service is removed, or after power reset.
401Moderate(Outdoor Unit) Either the compressor ran for more than 18 hours continuously trying to cool the home or the refrigerant pressure in the sys- tem is low.Compressor ran more than 18 hours to satisfy a single thermostat demand. Will not lockout system, if 2 stage, units with blinking LED light controls, unit will run in low speed; units with 7-segment display will display code, but continue to run in high speed. If a Heat Pump, and if outdoor temp is less than 65 degrees, code is ignored. Clears the error after 30 consecutive normal run cycles or power reset. Also monitors low pressure switch trips.
402Critical(Outdoor Unit) Either the discharge or suction pressure level is out-of-limits, or the is compressor overloaded.Discharge or suction pressure out-of-limits, or compressor overloaded. Clears the error after 4 consecutive normal compressor run cycles.
403Moderate(Outdoor Unit) The compressor ran for less than 3 minutes to satisfy a thermostat demand.Compressor runs less than 3 minutes to satisfy a thermostat demand. Clears the error after 4 consecutive normal run cycles or power reset.
408Critical(Outdoor Unit) The compressor is running continuously.Compressor runs continuously. Clears the error after 1 normal compressor run cycle or after power reset.
409Moderate(Furnace / Air Handler / Outdoor Unit) The secondary voltage for the (furnace, air-handier or outdoor unit) has fallen below 18VAC. If this continues for 10 minutes, the thermostat will turn off the (furnace, air-handier or outdoor unit).Secondary voltage is below 18VAC. After 10 minutes, operation is discontinued. Clears the code after voltage is higher than 20 VAC for 2 seconds or after power reset.
410Moderate(Outdoor Unit) The outdoor unit pressure is be- low the required limit.Unit pressures are below the lower limit. Pressure switch opens at 40 psig (system shuts down) and closes at 90 psig (system restarts).
411Critical(Outdoor Unit) The low pressure switch has opened 5 times during one cooling cycle. As a result, the thermostat has shutdown the outdoor unit.Open low pressure switch error count reached 5 strikes. Check system charge using approach and sub cooling temperatures. Reset by putting outdoor unit control in test mode or resetting low voltage power.
412Moderate(Outdoor Unit) The outdoor unit pressure is above the required limit. The system will shut down.Unit pressure is above the upper limit. Pressure switch opens at 590 psig (system shuts down) and closes at 418 psig (system restarts).
413Critical(Outdoor Unit) The high pressure switch has opened 5 times during one cooling cycle. As a result, the thermostat has shutdown the outdoor unit.Open high pressure switch error count reached 5 strikes. Check system charge using approach and sub cooling temperatures. Check outdoor fan operation. Check for dirt or debris blocking air flow to outdoor unit. Reset by putting outdoor unit control in test mode or resetting low voltage power.
414Critical(Outdoor Unit) The discharge line temperature is higher than the recommended upper limit of 279?F.Discharge line temperature is > 279?F. Make sure coil is clean and airflow unobstructed in and out of condenser. Check system operating pressures and compare to unit charging charts in installation manual. Clears after discharge temperature is < 225?F.
415Critical(Outdoor Unit) The discharge line temperature has been consistently higher than the recommended upper limit of 279?F.Discharge line high temperature error count reached 5 strikes. Make sure coil is clean and airflow unobstructed in and out of condenser. Check system charge using approach and sub cooling temperatures. Reset by putting outdoor board in test mode or resetting low voltage power.
418Moderate(Outdoor Unit) There is a faulty “W” output circuit.Faulty W output circuit.
419Critical(Outdoor Unit) The “W” output on the outdoor unit has reported more than 5 errors. As a result, the system has shutdown the outdoor unit.W output hardware fault count reached 5 strikes.
420Critical(Air Handler) The heat pump defrost cycle has taken more than 20 minutes to complete.Defrost cycle lasts longer than 20 minutes. Check heat pump operation. Cleared
when W1 signal is removed. Applicable only in communicating mode with non-communicating heat
421Critical(Outdoor Unit) The “W” output terminal on the outdoor unit is not wired correctly.Voltage sensed on W output terminal when Y1 out is deactivated.
700Moderate(Stat) The temperature sensor in the thermostat is not working properly.Recalibrate thermostat to clear. Replace thermostat if needed.
701Moderate(Stat) The thermostat is reading indoor temperatures above the pre-programmed limit.Recalibrate thermostat to clear; cool thermostat; adjust setpoint. Replace thermostat, if needed.
702Moderate(Stat) The thermostat is reading indoor temperatures below the pre-programmed limit.Recalibrate thermostat to clear; warm thermostat; adjust setpoint. Replace thermostat, if needed.
703Moderate(Stat) The humidity sensor in the thermostat is not working properly.Recalibrate thermostat to clear; adjust setpoint. Replace thermostat, if needed.
704Moderate(Stat) The thermostat is reading indoor humidity levels above the pre-programmed limit.Recalibrate thermostat to clear. Replace thermostat, if needed.
705Moderate(Stat) The thermostat is reading indoor humidity levels below the pre-programmed limit.Recalibrate thermostat to clear. Replace thermostat, if needed.
OhmThe ohm reading in the system is either too high or too low.Ohm reading between i+ and i- anywhere on the RSBus with supply power off should be between 70 and 90 ohms. If above 90 ohms, check and repair wiring, splices or other wiring defects that may be causing the excessive resistance. If less than 70 ohms, check for shorted wires.

Lennox X4146 thermostat troubleshooting

SymptomPossible CauseAction
Display does not come on.Thermostat is not being powered.Check to see that there is 24V between R and C terminals.
Check to see that batteries are properly installed.
Temperature settings do not change.Upper or lower temperature limits were reached.Check temperature setpoints.
Check installer set-up numbers 0600 and 0610. Modify, if necessary.
Keypad is fully locked.Check installer set-up numbers 0670 and change keypad lock option, if necessary.
Heating or cooling does not come on.Thermostat minimum-off time is activated.Wait up to 5 minutes for the system to respond.
System selection has not been set to heat or cool.Select proper system mode.
System type selection is incorrect.Check installer set-up number 0170 and make sure proper system type is selected.
Thermostat is calling for heat (Heat ON) or cool (Cool ON); but HVAC system is not operating.Heating or cooling equipment is not operating.Check wiring.
Check installer set-up number 0170 and make sure proper system type is selected.
Verify operation of equipment in system test mode.
Thermostat does not respond when touch screen is pressed.Keypad is fully locked.Check installer set-up numbers 0670 and change keypad lock option, if necessary.