51
Table 21. Lennox S40 Smart Thermostat Alert Codes and Troubleshooting
E2A=Errors to Action, GF= Gas Furnace, AH=Air Handler, IU=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OU=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system,
SRS=Smart Room Sensor, TS=Thermostat , IAQ- IAQ Monitor and WE=Wi-Fi Extender
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed Alert
Text Under dealer control
center > Notications
Component or System Operational State and Troubleshooting Tip
How to clear
alert code
105
Service Soon
/Service
Urgent
Communication
Problem
Low voltage wiring between one of the systems components has been compromised. The System
component (device) is unable to communicate.
• S40 - Open Dealer Service Center - Select the notication 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.
• Smart Technician APP - Select the Notications 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 C terminal on the indoor board as
shown in the installation and setup guide. See “Figure 5. Minimizing Electrical Noise” on page 6 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 S40 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
as shown in “Figure 12. Lennox S40, Lennox Communicating Indoor Controls and Float Switch” on page
12 . For testing purposes, remove oat switch from circuit.
• Inductive voltage from surrounding sources. Check each wire in AC mode to C on 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.
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