Lennox Error Code dF: Defrost mode (Furnace)

Updated October 15, 2026 · by Aurora Star Tech Inc.

Lennox error code dF on a furnace means: Defrost mode. It is also called Lennox diagnostic code dF.

Low severityFurnaceEL296UHV · Lennox SL280UHV · Lennox SL280UHNV · Lennox SL297NV · Lennox ML180UHE

Homeowner? What Lennox code dF means for you

Usually minor Your furnace is reporting: Defrost mode. This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.

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.
Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
Make sure the furnace front door or panel is closed properly; many furnaces will not run with the door switch open.
Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
Check that the gas valve next to the furnace is open (handle in line with the pipe). Do not force it.
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) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does Lennox error code dF mean?

Outdoor unit is in defrost. Normal behaviour in cold weather.

Applies to: EL296UHV(X) with control 103130-XX or 107045-XX

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

Lennox models that use code dF

Show all 34 models

EL296UH045XV36B EL296UH070XV36B EL296UH090XV36C EL296UH090XV48C EL296UH090XV60C EL296UH110XV48C EL296UH110XV60C EL296UH135XV60D ML180UH045E36AK ML180UH045XE36AK ML180UH070E36AK ML180UH070E36BK ML180UH070XE36AK ML180UH070XE36BK ML180UH090E48BK ML180UH090E60CK ML180UH090XE48BK ML180UH110E60CK ML180UH110XE60CK ML180UH135E60DK SL280UH060NV36A SL280UH070V36A SL280UH080NV48B SL280UH080NV60C SL280UH090V36B SL280UH090V48B SL280UH090V60C SL280UH100NV60C SL280UH110V60C SL280UH135V60D SL297UH040NV36B SL297UH060NV36B SL297UH080NV48C SL297UH080NV60C

Other Lennox Furnace codes

Code	Meaning
=	Two bars - soft disable
A	Blower airflow setting
c	Clear stored errors (inside error recall)
C1	Cooling, stage 1
C2	Cooling, stage 2
d	Dehumidification mode
E	Error recall mode (button menu)
E000	No error in memory
E105	Device communication problem
E106	Twin communication fault
E110	Low line voltage
E111	Line voltage polarity reversed

All Lennox Furnace error codes →

Lennox code dF: homeowner questions

What does Lennox code dF mean?

Defrost mode. Outdoor unit is in defrost. Normal behaviour in cold weather.

Is it safe to keep using my furnace with code dF?

Usually yes. Code dF is normally minor, but if it keeps coming back have it checked.

Can I reset Lennox code dF myself?

You can try one reset (power off for 30 seconds, then on). If Lennox code dF comes back, the cause is still there and a licensed technician should check it.

Who can fix Lennox code dF near me?

Aurora Star Tech Inc. repairs Lennox furnaces in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: Furnace Not Turning On: What to Check · Furnace Blinking Light: What the Flash Codes Mean

Troubleshooting guides

Blowing cold air All brands · Furnace
No heat All brands · Furnace
Short cycling All brands · Furnace
Blower motor does not run - Lennox SL280UHV ECM checks Lennox · Furnace
Clear stored error codes in the error recall menu Lennox · Furnace
Display shows two horizontal bars (soft disable) - Lennox SL297NV Lennox · Furnace
EL296UHV: normal gas heat sequence (what should happen after a call for heat) Lennox · Furnace
EL296UHV: what the display and the diagnostic button are telling you Lennox · Furnace
Furnace will not run (no heat) - Lennox EL195UHNE Lennox · Furnace
Furnace will not run (no heat) - Lennox SL297NV Lennox · Furnace
Furnace will not run - Lennox SL280UHV checklist Lennox · Furnace
Indoor blower does not run - Lennox EL195UHNE Lennox · Furnace
Indoor blower does not run - Lennox ML180UHE Lennox · Furnace
Poor ignition or combustion resonance - Lennox EL195UHNE Lennox · Furnace
Poor ignition or loud combustion resonance - Lennox SL280UHNV Lennox · Furnace
Program the unit size code on a replacement furnace control Lennox · Furnace
Recall or clear the last 10 error codes (red LED button) Lennox · Furnace
Test or reset the Low GWP refrigerant detection board (Test button) Lennox · Furnace
Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Furnace

Source: Lennox EL296UHV(X) Unit Information, Corp 1125-L5 (rev. 03/2022), Tables 4-5 (diagnostic modes and LED codes), printed p.32-33. 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.