Lennox 100017 User manual

1
LENNOX RESIDENTIAL COMMUNICATING SYSTEMS
ALERT CODE GUIDE (V2)
Alert Codes-Troubleshooting for Communicating Thermostats, Indoor and Outdoor Units, Lennox Smart
Zoning, Equipment Interface Module and PureAir S
100017
11/2022
LENNOX SMART THERMOSTAT
BASIC COMMUNICATION SYSTEM WIRING
AND ALERT CODES

2
1. Communication System Wirings
1.1. Communication Wiring Options
OPTION 1
Lennox Communicating
Outdoor Unit Lennox Communicating
Thermostat
Cut shield off at this end
Indoor Unit Communicating Control
(Using Shielded Wiring for Communication Lines)
18AWG
unshielded **
Shield (drain) wire MUST
be connected to indoor unit
common terminal.
OPTION 2
18 or 22AWG
shielded
Lennox Communicating
Outdoor Unit Lennox Communicating
Thermostat
18 or 22AWG
Standard Thermostat
Cable (4-Conductor)
Indoor Unit Communicating Control
(Using Non-Shielded Wiring)
Figure 1. Lennox Communicating System Wiring Connections using Unshielded (Option 1) or Shielded Wiring (Option 2) Cabling
There may be situations where alternate wirings methods may need to be employed. Two options are available to address an inductive voltage issue. If Alert Code
105 (see “Table 2. Alert Codes and Troubleshooting” on page 5) is still present after following troubleshooting Steps 1 and 2 then proceed to Step 3 wiring options
2 or 3.
• Option 2 - Using shielded 2-conductor cable between the indoor, outdoor and thermostat -i and +i terminals may be required.
• Option 3 - Using unshielded 2-conductor cable between the indoor, outdoor and thermostat -i and +i terminals may be required.
NOTE: When using multi-conductor unshielded thermostat cable, refer to “Figure 3. Minimizing Electrical Noise” on page 3.

3
Lennox
Communicating
Outdoor Unit
Lennox
Communicating
Thermostat
Indoor Unit Communicating Control
(Using 2-conductor Unshielded Cable for Communication Lines and
Separate 2-conductor Unshielded Cable for R and C)
OPTION 3
18/2 Brown Solid CU CL2 Thermostat Wire
Figure 2. Lennox Communicating System Wiring Connections using
Separate Unshielded Cable (Option 3)
1.2. Minimizing Electrical Noise
When using multi-conductor unshielded thermostat cable, to minimize electrical
noise, cap unused wires as illustrated below and run to indoor unit C terminal.
Single wire
to indoor unit
terminal “C”.
Unused
wires
Single wire directly to
C terminal or
to second bundle.
.
Indoor Unit Controller
Outdoor Unit
Thermostat
R i+ I- C
Unused
wires
Figure 3. Minimizing Electrical Noise
2. Soft Disable
Soft disabling is when the Lennox communicating thermostat nds an unknown
control on the S30/S40 system communication bus. The thermostat sends the
unknown control a message to go into soft disable mode until the component is
properly congured or removed.
Sometimes soft disable will occur when a control is being replace. Reconguring
the system should resolve this issue.
Lennox communicating thermostats will not show a alert code for a soft disabled
control. When soft disabling occurs only the control that has been disabled will
display the blinking LED status or seven-segment display indicator. Refer to the
device’s installation and setup guide for further guidance.

4
The Lennox communicating control with the soft disable state will indicate so as follows:
• On air handler, integrated furnace and outdoor controls, the soft disable state is display by double horizontal lines on seven segment display.
• On Lennox Smart Zoning damper control module and EIM the green LED will blink 3 seconds on and 1 second off.
Possible Cause
• Soft disable may occur when a control has been replace. Reconguring the system should resolve this issue.
• Sometimes Lennox communicating thermostat detects a new device or an existing device or a device on the system that is not communicating with the thermostat.
If this occurs, an alert code 10 is activated and the thermostat sends a soft disable command to the offending device on the communications bus (outdoor control,
IFC, AHC, EIM, or damper control module).
3. Notications (Service and Alert Codes)
These screens provide information on active notications and previously cleared notications. When selecting either a cleared or active notication a brief description
and alert code will be displayed. Notications are categorized by system, indoor unit (air handler or furnace), outdoor unit (air conditioner or heat pump), zoning
control (if installed) and thermostat.
3.1. Alert Code Priority Types and Notication Options
To expand a specication notication to access a more detail description of the alert code, press the down arrow to expand the description.
Table 1. Alert Code Priority Condition Visibility
Alert Priority Alert Priority Description n
Notications Displayed or Email Notications Sent
Displayed for
Homeowner on
Thermostat
Displayed
for Dealer on
Thermostat
Lennox®
Smart
Thermostat
Application
Lennox®Smart
Technician
Application**
LennoxPros
Service
Dashboard**
Homeowner
Emailed*
Dealer
Emailed
Service Urgent
Your system is in a No Heat/ No Cool or not
operating. Dealer service call is needed to get the
system running.
√ √ √ √ √ √ √
Service Soon /
Service Urgent
This alert priority indicates that the system will
likely recover on its own and no interaction is
necessary. Typically, either after a specic timer
period or a specic number of instances will
cause some Service Soon alerts to escalate to
Service Urgent.
X√X√ √ X X
Service Soon
System is not reaching set point or is partially
operating. A Dealer will need to service it with
24-48 hours.
X√X√ √ X X
Maintenance
Maintenance alerts are those intervals set as
reminders to change lters, replace UV lamps,
tune up systems.
√X√X√X X
Information
Only-Dealer
This alert priority is for information and is directed
to the dealer. X√X√X X X
* For homeowner to receive email notications, email updates has to be enabled. From the home screen, go to menu > user account > Email updates and set to ON.
** For dealers to receive service alerts and service alert email the feature needs to be enabled by the homeowner. From the S30 home screen, go to menu > user account > Dealer Email updates
and set to ON. From the S40 home screen go to Menu > User Account > Lennox Dealer Support Access > Dealer Support Access.

5
4. Alert Codes
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
10 Service
Urgent
Unknown
Device Detected
The thermostat when NOT in commissioning mode has detected an unknown device. Typically
the thermostat will send a command to the unknown device and place the device into a soft
disable state. The soft disable control will indicate so as follows:
• On air handler, furnace and outdoor controls, the soft-disabled state is displayed by double
horizontal lines on seven-segment display.
• On the damper control module, the green LED will ash 3 seconds on and 1 second off.
• On the equipment interface module, the green LED will ash 3 seconds on and 1 second off.
• A new communicating device has been added to the system since the original conguration setup
was completed.
• S30: Go to menu > settings > advanced settings > view dealer control center > equipment and
press reset all equipment. This will allow the system to auto-detect any Lennox communicating
devices attached.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Equipment Setting > Reset and select Reset Hvac Equipment. This will allow the system to
auto-detect any Lennox communicating devices attached.
Clear alert code by reconguring the
system.
11 Service
Urgent Missing Device
The thermostat cannot nd a previously installed system component.
• Check all system components (devices) connections to make sure they are Lennox communicating
compatible.
• Cycle system power.
• If problem persists, then check all system components (devices) connections to make sure they
are Lennox communicating compatible.
• S30: Go to menu > settings > advanced settings > view dealer control center > equipment and
press reset all equipment. This will allow the system to auto-detect any Lennox communicating
devices attached.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Equipment Setting > Reset and select Reset Hvac Equipment. This will allow the system to
auto-detect any Lennox communicating devices attached.
Cycle system power, and If problem persists
then clear by reconguring the system.

6
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
12 Service
Urgent
Indoor Unit Not
Detected
Thermostat did not nd an indoor unit. Make sure there is an Lennox communicating indoor unit
on the system.
• Check for voltage and missing component.
• Check R, i+,i- and Cconnections at mag-mount or subbase, smart hub and all attached
communicating components.
• Ohm wires for electrical continuity.
• Cycle power to both indoor unit rst and then thermostat.
• Verify that equipment interface module (if applicable) is congured as either an air handler or
furnace when used with a non-communicating indoor unit.
• S30: Go to menu > settings > advanced settings > view dealer control center > equipment and
press reset all equipment. This will allow the system to auto-detect any Lennox communicating
devices attached.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Equipment Setting > Reset and select Reset Hvac Equipment. This will allow the system to
auto-detect any Lennox communicating devices attached.
• Replace indoor unit control if there is no response.
Automatically clears when the system
detects that the issue no longer exists.
13 Service
Urgent
Duplicate
Comfort Sensor
ID
Thermostat found more than one outdoor unit, or more than one indoor unit, or more than one
thermostat connected to the system. Thermostat will display the message “Too Many Devices of
the Same Type”.
• Check wiring and remove duplicate equipment.
• S30: Go to menu > settings > advanced settings > view dealer control center > equipment and
press reset all equipment. This will allow the system to auto-detect any Lennox communicating
devices attached.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Equipment Setting > Reset and select Reset Hvac Equipment. This will allow the system to
auto-detect any Lennox communicating devices attached.
Automatically clears when the system
detects that the issue no longer exists.
14 Service
Urgent
Too Many
Devices of the
Same Type
The thermostat found more than one thermostat, indoor or outdoor unit on the system.
• Check wiring and remove duplicate equipment.
• S30: Go to menu > settings > advanced settings > view dealer control center > equipment and
press reset all equipment. This will allow the system to auto-detect any Lennox communicating
devices attached.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Equipment Setting > Reset and select Reset Hvac Equipment. This will allow the system to
auto-detect any Lennox communicating devices attached.
Automatically clears when the system
detects that the issue no longer exists.
15 Information
Dealer Only
Parameter
Mismatch
Detected
Incorrect parameter settings detected. Dealer would need to re-set the system and start congura-
tion again.
Automatically clears once proper system
conguration is completed.
20 Service
Urgent
Protocol
Upgrade
Required
The thermostat cannot work with one of the system devices because the thermostat rmware
needs to be updated rst. Update thermostat rmware.
21 Service
Urgent
Incompatible
Equipment
Detected
Equipment is trying to be utilized that is not compatible with other system components, such as a
single-stage non-variable speed motor furnace with a modulating outdoor unit. Use compatible equipment.

7
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
29 Service
Urgent
Over
Temperature
Protection
The thermostat is reading an indoor temperature that is higher than 90ºF (factory default). The
thermostat will not allow any heating operation to begin until it senses an indoor temperature lower
than 90ºF. Indoor temperature rose above 90ºF 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 below 90ºF.
Automatically clears when the system
detects that the issue no longer exists.
30 Service
Urgent
Low
Temperature
Protection
The thermostat will not allow any cooling operation to begin until it senses a temperature higher
than 40ºF.
• 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 40ºF.
Automatically clears when the system
detects that the issue no longer exists.
31 Service
Urgent
Lost
communication
with Device
The applicable system component (indoor, equipment interface, damper control module or outdoor
unit) has not communicated with thermostat for more than three minutes.
• Check connections and voltages.
• Ohm wires for electrical continuity.
• If oat switch is installed on air handler drain pain, check condensate line to ensure it is not
clogged and tripping the oat switch connected in series with Rterminal.
• Check to see if freezestat is installed.
If fault persists, then cycle power.
Fault clears after communication is
restored.
32 Information
Only-Dealer Device Resetting
The applicable system component (device) is resetting itself. This issue may occur during a power
outage or power uctuation in the system. If persistent or if it coincides with the system operations
then proceed with the following troubleshooting steps.
• Check the power connections.
• Check the amperage draw at the transformer (possible overloaded).
• Check 24VAC voltage at the system component (device).
• If the fault persists after checking the connections, replace the applicable control.
To clear the alert code, go to menu > set-
tings > advanced settings > view dealer
control center > notications and select
the alert code and press the clear button.
34 Service
Urgent
Must Program
Unit Capacity
For Device
The thermostat does not know the capacity (tonnage) of the indoor or outdoor unit. The applicable
system component is missing the programmed unit capacity.
• Remove power to thermostat before programming the unit control.
• Go to applicable unit control and program the unit capacity manually (see the unit installation
instruction for conguration instructions).
• Once conguration is complete then reconnect thermostat wires.
• S30: Go to menu > settings > advanced settings > view dealer control center > equipment and
press reset all equipment. This will allow the system to auto-detect any Lennox communicating
devices attached.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Equipment Setting > Reset and select Reset Hvac Equipment. This will allow the system to
auto-detect any Lennox communicating devices attached.
Automatically clears when the system
detects that the issue no longer exists.

8
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
35 Service
Urgent
Incorrect
Operation Of
Device
• Message sent by thermostat to unit after more than 15 minutes asking for initiating heating or cooling with no response from unit.
• Message sent by thermostat to unit after more than 15 minutes asking for termination of heating or cooling with no response from unit.
Result
A communicating device in the system has been disabled due to a fault/lockout code in the unit’s control.
Another possible cause is electrical noise interference affecting the communicating system when the compressor contactor coil is energized.
Corrective Action:
• Communicating system: Wire a transient voltage suppressor in parallel with the compressor contactor coil terminals on the outdoor unit.
• Non-communicating outdoor unit: Wire transient voltage suppressor (89W72) in parallel with compressor contactor coil or across the Y1 and C
terminals on the indoor unit control.
NOTE: See service and application note IAQ-10-01 for further details.
Transient Voltage Suppressor Part information: Made by Little Fuse, part number 5KP43CA bidirectional Transorb aka TVS Diode. Please con-
tact your FTC or inside technical support for help in acquiring the transient voltage suppressor if not available in your local electronics store.
36 Service
Urgent
Heating when
Not Requested
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.
• S30: Go to menu > settings > advanced settings > dealer control center > diagnostics and
press the start diagnostics button.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Diagnostics and select Select All and the secure Start button.
• Check for other alert codes that may be preventing the system from operating as expected.
• Check all heating equipment to determine cause of heating demand.
• Recycle power.
Automatically clears when the system
detects that the issue no longer exists.
37 Service
Urgent
Cooling when
not Requested
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.
• S30: Go to menu > settings > advanced settings > dealer control center > diagnostics and
press the start diagnostics button.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Diagnostics and select Select All and the secure Start button.
• Check for other alert codes that may be preventing the system from operating as expected.
• Check all cooling equipment to determine cause of cooling demand.
• Recycle power.
Automatically clears when the system
detects that the issue no longer exists.

9
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
38 Service
Urgent
Not Heating
when Requested
The system has not been able to turn on the heating for more than 45 minutes.
• The system will go off-line for 60 minutes and will attempt to restart itself.
• Run the system in diagnostic mode and verify that it matches actual equipment operation.
• S30: Go to menu > settings > advanced settings > dealer control center > diagnostics and
press the start diagnostics button.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Diagnostics and select Select All and the secure Start button.
• Check for other alert codes that may be preventing the system from operating as expected.
• Check all heating equipment to determine cause.
• Recycle power.
Automatically clears when the system
detects that the issue no longer exists.
39 Service
Urgent
No Cooling
when Requested
The system has not been able to turn on the cooling for more than 45 minutes.
• The system will go off-line for 60 minutes and will attempt to restart itself.
• Run the system in diagnostic mode and verify that it matches actual equipment operation.
• S30: Go to menu > settings > advanced settings > dealer control center > diagnostics and
press the start diagnostics button.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center >
Diagnostics and select Select All and the secure Start button.
• Check for other alert codes that may be preventing the system from operating as expected.
• Check all cooling equipment to determine cause.
• Recycle power.
This alert code will automatically clear when
the system detects the issue no longer
exists.

10
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
40 Information
Only-Dealer HP Heating Lockout.
The heat pump could not increase the room temperature 0.5°F towards the set point in 30 minutes.
Gas Furnace Heating
In order to use the gas furnace as a primary heating source (not defrost tempering) when the outdoor temperature is between the high and low
balance points, the heat pump:
• Must be used for a minimum of 30 minutes and the temperature in the zone not increase by more than 0.5°F
• Has not gone into defrost in the 30 minute period.
The default for HP Heating Lockout Time default is 120 minutes and will lock the heat pump off when the outdoor temperature is above the high
balance point. Selectable range is 60 to 240 minutes.
• S30: Go to menu > settings > advanced settings > dealer control center > equipment > smart hub and located HP Heating Lockout Time
to verify the lockout time setting.
• S40: Go to Menu > Settings > Advanced Settings > View Service Support Center > Equipment Settings > Thermostat and located HP
Heating Lockout Time to verify the lockout time setting.
• Check air ow to the zones or zones.
• Check discharge air temperatures.
• Check calibration of room thermostat.
Outdoor Unit and Zoning
When the heat pump could not get a zone thermostat to progress 0.5°F towards the set point in 30 minutes the system will lock out the heat
pump and switch to the secondary heat source. Electric heat or if in dual-fuel applications the furnace will be used and the system put in heat
pump heating lockout timer) default is 120 minutes. It will lock the heat pump off and the gas furnace will nish the heating cycle
Set the low balance point and high balance point as close together as possible. (This is a 3°F difference – Example: set high balance point at
25°F and low balance point would set at 22°F). Below the low balance point, the furnace will heat the home / between the low and high balance
point, the heat pump and furnace will heat the home. When the outdoor temperature is above the high balance point, the gas furnace is locked
out and all the heat is provided by the heat pump.
41 Information
Only-Dealer Device Control Board Replaced
This alert code will appear anytime a communicating control [Furnace, air handler, PureAir S,
damper control module, air conditioner or heat pump] is replaced in the system. Must be cleared manually.

11
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
105 Service
Urgent
Communication
Problem
Low voltage wiring between one of the systems components has been compromised. The system
component (device) is unable to communicate.
• Open Dealer Service Center - Select the notication icon, select All, review alert code details
to determine which device’s low voltage wiring is experiencing a communication issue. Review
both active and cleared alerts.
• S40 Smart Technician App - Select the Notications icon, select All, review alert code details
to determine which device’s low voltage wiring has the communication problem. Review both
active cleared alerts.
Step 1 Troubleshooting:
In most issues can be resolved by taking the following actions:
• Make sure all unused wires are tied together and taken back to the Cterminal on the indoor
board as shown in the installation and setup guide. See “1.2. Minimizing Electrical Noise” on
page 3 for illustration on bundling unused wires to common.
• Check for loose terminal connections on components (devices). Lennox recommends using a
slotted screwdriver with a 3/32” (2.4 mm) tip.
• Check for incorrectly wired or poorly spliced connections between components.
• Verify that low voltage going to system components has been separated from high voltage
wiring in wall, ceiling, & oor cavities.
• Check for proper grounding on the line voltage and low voltage wiring, transformer, and
equipment.
If Alert Code 105 is still present after performing the actions listed above proceed to Step 2:
Troubleshooting.
Step 2 Troubleshooting:
• Disconnect all wiring to other components (except thermostat and indoor unit) and reconnect
one device at a time. Recommission system each time a device is added until wiring issue has
been located.
• Zoning: If a zoning system has been installed and is wired directly from the thermostat to the
zoning control then disconnect wiring and run control wiring from the zoning control directly to
the indoor unit control. Wiring diagrams are provided in the Lennox Smart Zoning Installation and
Setup Guide.
• Float Switch: When using a oat switch, use an isolation relay between the dedicated oat switch
terminals (see thermostat installation and setup guide). For testing purposes, remove oat switch
from circuit.
• Inductive voltage from surrounding sources. Check each wire in AC mode to Con circuit board.
> Good voltage is .03-.3VAC inductive voltage is not an issue.
> Acceptable can be up to .7VAC with moderate success.
> Some units have worked with up to 1.2VAC with occasional success.
> Voltage over 1.2VAC needs to be addressed.
If Alert Code 105 is still present after performing the actions listed above proceed to Step 3:
Troubleshooting.
Automatically clears when the system
detects the issue no longer exists.

12
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
105
Service Soon
/Service
Urgent
Communication
Problem
Step 3 Troubleshooting:
New low voltage wiring will need to be ran to the system components. There are 2 options for
replacing low voltage wiring:
• OPTION 2 - Utilizing 18/2 AWG for wires going to 24VAC (Rand C) terminals and 18 or 22/2
AWG shielded wires going communicating terminals (i+ and i-).
• OPTION 3 - Utilizing two separate 18/2 AWG unshielded wires. One set wire to 24 VAC terminals
(Rand C) and one set to communicating terminals (i+ and i-).
• See “1.1. Communication Wiring Options” on page 2 for Option 2 and 3 wiring diagrams.
Automatically clears when the system
detects the issue no longer exists.
110 Service
Urgent
GF Low AC Line
Voltage
The component AC line voltage is too low. This alert code may appear during a brownout.
• It may also occur when line voltage is below its designed operating value.
• Check and correct the power line voltage.
Automatically clears when the system
detects the issue no longer exists.
111 Service
Urgent
GF Line Polarity
Reversed
The unit is reporting that its power and neutral lines are reversed.
• Turn off the power to the system and correct the line power voltage wiring.
• System resumes normal operation ve seconds after service urgent condition is recovered.
Automatically clears when the system
detects the issue no longer exists.
112 Service
Urgent
GF No Ground
Connection
The reporting component cannot nd earth ground. The thermostat will shut down the system.
• Provide proper earth ground to the equipment.
• System resumes normal operation ve seconds after service urgent condition is recovered.
Automatically clears when the system
detects the issue no longer exists.
113 Service
Urgent
GF High AC
Line Voltage
Line voltage high (voltage higher than nameplate rating).
• Provide power voltage within proper range.
• System resumes normal operation ve seconds after service urgent condition is recovered.
Automatically clears when the system
detects the issue no longer exists.

13
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
114
Service
Soon/Service
Urgent
AC Line
Frequency /
Distortion Prob
In most cases the errors will have something to do with the transformer(s) phasing, input power or output loading (amperage load).
For the air handler control only, alert code 114 is generated only if the measured line frequency is below 57Hz or above 63Hz and remains out of
range for 10 consecutive seconds. We count power line cycles and determine line frequency every one second of time based on the processor’s
quartz crystal oscillator. We have a fair amount of ltering on when we consider a power line cycle to have occurred, so there would have to be
really bad distortion for it to count an extra cycle or miss a real cycle.
Voltage low enough to miss a cycle would generate an alert code 115. There are lots of events, such as power utility substation switching, that
could occasionally make our power line frequency off by one count. These are rare one-time events and I don’t know anything other than a
generator with bad frequency that could cause problems long enough to cause this alert code.
There is a frequency / distortion problem with the power to a specic system component. This alert code may indicate transformer overload-
ing.
• 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 will resume normal operation ve seconds after fault recovered.
• All applicable system component outputs are disabled – service soon condition.
• After 10 minutes, the priority condition is escalated – service critical condition.
• Damper control module will operate in central mode only until the proper voltage is restored or frequency distortion is resolved.
• If connected to Lennox Smart Zoning, set damper control module transformer jumper to system transformer. Check for proper wiring. Replace
40VAC furnace transformer with 70VAC transformer. Re-commission system.
NOTE: The unitary control (outdoor unit control board) whether it is a single, two-stage or multi-stage control is not displaying alert code 114.
115 Service
Urgent
Low Secondary
(24VAC) Voltage
24VAC power to a system component control is lower than the required range of 18 to 30VAC.
• Check and correct voltage.
• Check for additional power-robbing system components (devices) connected to system.
• This alert code may require the installation of an additional or larger VA transformer.
• Damper control module will operate in non-zone mode until proper voltage is restored.
Automatically clears when the system
detects the issue no longer exists.
116 Service Soon
ID High
Secondary
(24VAC) Voltage
• Thermostat will display this code when 24VAC power is high (18 to 30VAC).
• Will display Furnace or Air Handler High Secondary (24VAC) voltage.
Check and correct voltage. Check for proper
line voltage (120VAC, 240VAC, etc.) to
equipment. Clears when control senses
proper voltage.
117 Service Soon ID Poor Ground
The reporting unit has poor earth grounding.
• Provide proper grounding for the system component (device).
• Check for proper earth ground to the system.
• Reference Corp0123L10 for additional information
Automatically clears 30 seconds after the
issue is corrected.

14
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
120 Service Soon Unresponsive
Device
There is a delay in the system component responding to the system. Typically this alert code does
not cause any operational issues and will clear on its own.
• This alert code is usually caused by a delay in the outdoor unit responding to the thermostat.
• Leaking voltage from strands within the bundle.
> Land only the R wire on the R terminal to load the bundle with 24VAC.
►Typically only the R wire needs to be landed to identify if voltage is leaking.
►If voltage is present checking the other wires is informational only but not needed.
►If voltage is not present checking the other wires one at a time would be needed.
> Check each loose wire in AC mode to Con circuit board.
►Good voltage is .03 -.3VAC leaking voltage is not the issue.
►Acceptable can be up to .7VAC with moderate success.
►Some units have worked with up to 1.2VAC with occasional success.
►Voltage over 1.2VAC needs to be addressed.
Automatically clears after an unresponsive
system component (device) responds to any
inquiry.
124 Service
Urgent
Tstat Lost
Communication
To Smarthub
The thermostat has lost communication with a system component for more than three minutes.
• Check the wiring connections between components.
• Ohm wires.
• Cycle power.
• Any component that is miss-wired may cause a false component code to be shown on system
component.
• Disconnect all wiring to other system components and check communication one at a time.
NOTE: When using a oat switch, use isolation relay to break common wire to outdoor unit. For
testing purposes, remove oat switch from the circuit
This alert code stops all associated system operations and waits for a heartbeat message from
the system component that is not communicating.
Automatically clears after communication
is re-established with applicable system
component (device).
125 Service
Urgent
Control
Hardware
Problem
There is a hardware problem on a system component control.
• In system using Lennox Smart Zoning zoning, the system will remain in non-zone mode (all
dampers open) for ve minutes after priority condition no longer exist.
• In systems using a Equipment Interface Module, remove jumper if present on indoor unit between
Rand W2.
• In systems using a PureAir S, the pure air control board jumper selector is missing.
If none of the above tips are applicable, then replace the control if the problem prevents operation
and is persistent.
Automatically clears ve minutes after the
issue no longer exists.

15
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
126 Service
Urgent
Control Internal
Communication
Prob
There is an internal hardware problem on the system component control. In addition, if you have
zoning the alert code is triggered when your zone temperature is deviating away from set point
persistently.
• Typically the system component control will reset itself.
• Replace the system component (device) control if the problem prevents operation and is
persistent.
Automatically clears 300 seconds after the
issue no longer exists.
130 Service
Urgent
Conguration
Jumper Missing
• Conguration jumper missing on equipment interface module (EIM).
• Conguration jumper missing on air handler communicating control board 1
• Install the missing jumper.
• Set as heat pump, furnace control or air handler control for EIM.
NOTE: This is applicable in non-communicating applications only.
Automatically clears after the missing or
incorrectly installed jumper is installed or
corrected.
132 Service
Urgent
Device Control
Software Fault
System component control software is corrupted.
• Recycle power.
• If failure re-occurs, replace the system component control.
Manual system power reset is required to
recover from this alert code.
180 Service Soon
Outdoor
Temperature
Sensor Problem
The thermostat has found a problem with the outdoor sensor in the outdoor unit or the optional
outdoor sensor connected to the indoor unit. In normal operation after system component control
recognizes sensors, the alert code will be sent if valid temperature reading is lost.
• Compare outdoor sensor resistance to temperature / resistance charts in unit installation
instructions.
• Replace sensor pack or stand alone outdoor sensor.
• At the beginning of (any) conguration, furnace, air-handler control or equipment interface
module will detect the presence of the sensor(s).
• If detected (reading in range), appropriate feature will be set as ‘installed’ and shown in the
‘About’ screen.
Automatically clears upon conguration, or
sensing normal values.
181 Service Soon
OD Suction
Pressure
Transducer
Fault
• Suction Pressure Transducer reading above 4.75V or below 0.25V for 24hrs +/- 3hrs. Run on
staged operation.
Resets after 3 consecutive readings that are
in range
182 Service Soon
OD Suction
Temperature
Sensor Fault
• Reading below 0.25V or above 4.75V for 24hrs +/- 3hrs. System will continue to operate normally. Resets after 3 consecutive readings that are
in range
183 Service Soon
OD Liquid
Pressure Sensor
Fault
• Under 0.25V and above 4.75V readings for 24 hours +/-3hrs or more on the sensor will cause
this error.
• Continue normal operation, see sections related to low pressure switch emulation for specic
details related to low pressure switch faults.
Resets after 3 consecutive readings that are
in range
184 Service Soon
OD LIquid
Temperature
Sensor Fault
• Sensor shorted or open for 24 hours +/-3hrs or more.
• Continue normal operation.
Resets after 3 consecutive readings that are
in range

16
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
200 Service
Urgent
GF Rollout Limit
Switch Open
The furnace roll out limit switch is open. Correct the cause of roll out trip.
• Reset roll out switch.
• Test the furnace operation.
• Check for blocked or obstructed vent pipe (Intake and/or Exhaust).
• Check for ame stability, if ame is unstable, look for cause.
Automatically clears after the furnace roll
out switch is closed.
201 Service
Urgent
ID Blower Motor
Fault
Lost communication with indoor blower motor.
• Possible causes include power outage, brown-out, motor not powered, loose wiring, condensation
on system component control without cover on breaker.
• Problem may be on system component control or motor side.
Automatically clears after communication is
restored.
202 Service
Urgent
ID Blower Motor
& Unit Size
Mismatch
The unit size code for the indoor unit and the size of blower motor do not match. Incorrect appli-
ance unit size code selected.
• Remove the thermostat from the system while applying power and reprogramming.
• Check for proper conguring under unit size codes for furnace/air handler in conguration guide
or in installation instructions.
Automatically clears after the correct match
is detected following a reset.
203 Service
Urgent
ID Invalid Size
Unit Code
The unit size code for the indoor unit has not been selected or set incorrectly.
• Verify that the correct unit size code is congured. Unit size codes for furnace and air handler are
listed in the system component conguration guide or installation instruction.
• Remove the thermostat from the system while applying power and set the unit size code per
instructions provided in the indoor unit installation instruction.
Automatically clears after the correct match
is detected following a reset.
204 Service
Urgent
GF Check Gas
Valve
There is an issue with the furnace gas valve.
• Check gas valve operation and wiring.
• Check for voltage to the gas valve.
Automatically clears after the issue is
corrected.
205 Service
Urgent
GF Gas Valve
Relay Contact
Closed
The furnace gas valve relay contact is closed.
• Check wiring on control and gas valve. The relay is located on the furnace control .
• If issue continues replace furnace control.
Automatically clears after the issue is
corrected.
206 Service Soon
GF Gas Valve
2nd Stage Relay
Fault
The furnace gas valve second-stage relay is faulty.
• Furnace will operate on rst-stage for the remainder of the heating demand.
• If unable to operate second-stage, replace furnace control.
Automatically clears after the issue is
corrected.
207 Service
Urgent
GF HSI Sensed
Open
The furnace hot surface igniter is open.
• Measure the resistance of hot surface igniter.
• Replace the igniter if it is not within the specied range found in furnace installation instruction.
Automatically clears after the issue is
corrected.

17
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
223 Service Soon
GF Low
Pressure Switch
Open
The furnace low pressure switch is open.
• Check pressure (inches w.c.) of the low pressure switch closing during a heat call.
• Measure operating pressure (inches w.c.).
• Inspect vent for blockages and combustion air inducer for correct operation and restriction.
• Check for blocked cold end heater box or condensate drain or drain strainers at outlet of cold
end heater box.
• Check for cracked hoses.
• Check levelness of unit.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Automatically clears after the issue is
corrected.
224 Service
Urgent
GF Low
Pressure Switch
Stuck Closed
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 for blockage and combustion air inducer for correct operation and restriction.
• Check for moisture in pressure switch.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Other possible issues that are specic to the older Lennox communicating thermostats are as
follows:
• Alert code is generated when a subsequent heating call occurs within 30 seconds of a prior call
for heat ending.
• If a call for heat occurs during this time period, the inducer post-purge from the previous call may
still be in process. If that condition exists, the IFC will sense the pressure switch circuit is closed
therefore activating the alert code 224 and generate an email notication.
• Once the fault is cleared, typically seconds after being generated, the subsequent call for heat
will be initiated and the furnace will return to normal operation.
• Lennox has not received any complaints of no heat situations associated with this operating
condition. It has been determined that occasionally the fault clears itself and the alert code is not
stored in the IFC or Lennox communicating thermostat.
Automatically clears after the issue is
corrected.
225 Service Soon
GF High
Pressure Switch
Failed to Close
The furnace high pressure switch will not close.
• Check pressure (inches w.c.) of high pressure switch closing during a heat call.
• Measure operating pressure (inches w.c.).
• Inspect vent for blockage and combustion air inducer for correct operation and restriction.
• Check for blocked cold end heater box or condensate drain or drain strainers at outlet of the cold end heater box.
• Check cracked hoses
• Check levelness of unit.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace Pressure Switch Troubleshooting” for additional
information.

18
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
226 Service
Urgent
GF High
Pressure Switch
Stuck Closed
The furnace high pressure switch will not open.
• Check operation of high pressure switch closing during a heat call.
• Measure operating pressure (inches w.c.).
• Inspect vent for blockage and combustion air inducer for correct operation and restriction.
• Check for moisture in pressure switch.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Automatically clears after the issue is
corrected.
227 Service Soon
GF Low
Pressure Switch
Open in Run
Mode
The furnace low pressure switch is open while 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 for blockage and combustion air inducer for correct operation and restriction.
• Check for blocked cold end heater box or condensate drain or drain strainers at outlet of cold
end heater box.
• Check for cracked hoses.
• Check levelness of unit.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Automatically clears after the issue is
corrected.
228 Service Soon GF Inducer
Calibration Issue
The furnace control is not able to calibrate the pressure switch. Unable to perform pressure switch
calibration.
• Inspect vent for blockage and combustion air inducer for correct operation and restriction.
• Check for blocked cold end heater box or condensate drain or drain strainers at outlet of cold end
heater box (CEHB).
• Check for cracked hoses.
• Check levelness of unit.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Automatically clears after a successful
calibration.
229 Information
Only-Dealer Ignition on High Fire
• Furnace control switched to high re ignition because low re pressure switch did not close in
allowed time.
• Early models only - If fan is on when call for W1 is initiated; unit will re on high re for 60 seconds
before dropping down to low re.
No action is required.

19
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
240 Service Soon
GF Low Flame
Current - Run
Mode
This could be either low ame current or a loss of ame while in run mode.
• Check micro-amperes of the ame sensor using thermostat or control board.
• Clean or replace the ame sensor.
• Measure voltage of neutral to ground to ensure good unit ground.
• Clean face of burner assembly.
• Conrm that the vent termination is properly installed and not re-circulating.
• Check for loose a wiring connection at gas valve.
NOTE: Refer to Service and Application Note H-14-06“ Flame Rectication In All Gas Furnaces”
for additional information.
Automatically clears after a proper micro-
amp reading has been sensed.
241 Service
Urgent
GF Flame Out of
Sequence-Still
Present
Flame sensed without call for gas heating. Perform the following:
• Shut off gas.
• Check for a gas valve leak.
• Check for voltage to gas valve.
Replace the gas valve if needed.
Automatically clears when a heat call ends
successfully.
250 Service Soon
GF Primary
Limit Switch
Open
The furnace primary limit switch is open. If limit switch is not closed within three minutes, the unit
will go into a 60 minute soft lockout (Watchguard mode). Perform the following:
• Check for high gas pressure.
• Check for low supply air. Low supply air due to being plugged or restriction in system (example:
dirty air lter or blockage in duct work).
• Check for proper ring rate on furnace.
• Check for non-functioning zone dampers.
NOTE: Limit trips will place the Lennox Smart Zoning zoning system into non-zone mode.
NOTE: See ACC-14-01 for further details.
Automatically clears when a heat call ends
successfully.
NOTE: If this issue occurred on an Lennox
Smart Zoning zoning system, the eld will
need to manually activate the zoning.
252 Service Soon
ID Discharge
Air Temperature
High
A discharge air-temperature is high. Perform the following:
• Check temperature rise, air ow and input rate.
• Check for dirty air lter(s).
NOTE: See Service and Application Note ACC-14-01 for further details.
Automatically clears when a heat call ends
successfully.
270 Service
Urgent
GF Flame Failed
To Ignite
The furnace is in Watchguard mode. The furnace igniter cannot turn on the ame. This is a ve
strike condition during a single demand.
• Check for proper gas ow.
• Ensure that igniter is lighting burner.
• Check ame sensor current.
• Check for dirty lters.
• Check for blocked cold end heater box or condensate drain and cracked hoses.
Automatically clears on successful igni-
tion.

20
Table 2. Alert Codes and Troubleshooting
GF= Gas Furnace, AH=Air Handler, ID=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OD=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system and TS=Thermostat
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed
Alert Text
Under dealer
control center >
Notications
Component or System Operational State and Troubleshooting Tip How to clear alert code
271 Service
Urgent
GF Low Press
Switch Open
The furnace is in Watchguard mode. The furnace low pressure switch is open. This is a ve strike
condition during a single demand.
• Check pressure (inches w.c.) of low pressure switch closing during a heat call.
• Measure operating pressure (inches w.c.).
• Check for blocked cold end heater box (CEHB), or condensate drain or drain strainers at outlet
of CEHB and cracked hoses.
• Check for cracked hoses.
• Check levelness of unit.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Automatically clears on successful igni-
tion.
272 Service
Urgent
GF Low Press
Switch Open
Run Mode
The furnace low pressure switch is open during run mode. The system will go into Watchguard
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 for blockages, and combustion air inducer for correct operation and restriction.
• Check for blocked cold end heater box (CEHB), or condensate drain or drain strainers at outlet
of CEHB and cracked hoses.
• Check for cracked hoses.
• Check levelness of unit.
NOTE: Check Service Manual and Service and Application Note H-13-07 “Condensing Furnace
Pressure Switch Troubleshooting” for additional information.
Automatically clears when a heat call ends
successfully.
273 Service
Urgent
GF Flame Fail In
Run Mode
The furnace ame is going off during a heating cycle. The system will go into Watchguard
mode.
• Check micro-amperes of ame sensor using thermostat or control diagnostics.
• Clean or replace sensor.
• Measure voltage of neutral to ground to ensure good unit ground.
• Clean face of burner assembly.
Automatically clears when a heat call ends
successfully.
274 Service
Urgent
GF Primary
Limit Switch
Open
The furnace limit switch has been open for more than three minutes. The system will go into
Watchguard mode. In Lennox Smart Zoning zoning systems, the limit trips will place the system
into central mode.
• Check for high gas pressure.
• Low supply air due to being plugged or restriction in system (example: dirty air lter or blockage
in duct work).
• Check for proper ring rate on furnace.
• Check for non-functioning zone dampers.
NOTE: Refer to Service and Application Note ACC-14-01 - Lennox Smart Zoning®and SLP98 -
Insufcient Zone Heating and Alert Code 250 Issues for corrective actions.
Automatically clears when a heat call ends
successfully.