Lennox Error Code 35: Incorrect operation of device (AC)
Lennox error code 35 on a air conditioner means: Incorrect operation of device. It is also called Lennox diagnostic code 35.
Homeowner? What Lennox code 35 means for you
Call a technician Your air conditioner is reporting: Incorrect operation of device. The air conditioner has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Check both breakers and the outdoor disconnect box beside the outdoor unit; all should be ON.
- Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
- Keep about 2 feet around the outdoor unit clear of leaves, grass and debris.
- If you see ice on the pipes or the indoor coil, turn the system off and run only the fan for a few hours, then call a technician.
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Lennox error code 35 mean?
The unit did not respond within 15 minutes to a thermostat request to start or stop heating/cooling; a device was disabled by a fault/lockout, or electrical noise from the contactor coil disrupted communication. S30/S40 thermostat alert code 35.
Applies to: Lennox communicating air conditioners incl. variable-capacity inverter units in S30/S40 smart thermostat systems
Common causes of Lennox code 35
- Device in fault/lockout
- Electrical noise when the compressor contactor coil energizes
Lennox models that use code 35
EL16KC1-018-230AEL16KC1-024-230AEL16KC1-030-230AEL16KC1-036-230AEL16KC1-041-230AEL16KC1-042-230AEL16KC1-047-230AEL16KC1-048-230AEL16KC1-060-230A
Other Lennox AC codes
All Lennox Air Conditioner error codes →
Lennox code 35: homeowner questions
What does Lennox code 35 mean?
Incorrect operation of device. The unit did not respond within 15 minutes to a thermostat request to start or stop heating/cooling; a device was disabled by a fault/lockout, or electrical noise from the contactor coil disrupted communication. S30/S40 thermostat alert…
Is it safe to keep using my air conditioner with code 35?
It depends on the cause. The air conditioner has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Can I reset Lennox code 35 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code 35 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code 35 near me?
Aurora Star Tech Inc. repairs Lennox air conditioners in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: AC Running But Not Cooling: What to Check
Troubleshooting guides
- Not cooling All brands · Air Conditioner
- Low cooling capacity - check airflow and charge - Lennox EL16KC1 Lennox · Air Conditioner
- Outdoor unit will not start - Lennox EL16KC1 Lennox · Air Conditioner
- RDS leak-detected mode and start-up test - Lennox EL16KC1 Lennox · Air Conditioner
- Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Air Conditioner
Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.11. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.