Lennox Error Code Green LED 3 s on / 1 s off: Soft disable – zoning damper module or EIM (Furnace)

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

Lennox error code Green LED 3 s on / 1 s off on a furnace means: Soft disable - zoning damper module or EIM. It is also called Lennox diagnostic code Green LED 3 s on / 1 s off.

Low severityFurnace

Homeowner? What Lennox code Green LED 3 s on / 1 s off means for you

Usually minor Your furnace is reporting: Soft disable - zoning damper module or EIM. 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 Green LED 3 s on / 1 s off mean?

On a Smart Zoning damper control module or an equipment interface module (EIM), the green LED blinks 3 seconds on and 1 second off. The thermostat found a device on the communication bus that it does not recognise and has parked it in soft disable until it is configured or removed. The thermostat itself shows no alert code for this; only the affected control shows the indicator. Often seen after a control is replaced.

Applies to: Lennox S30/S40 communicating systems: communicating furnaces, air handlers, outdoor units, Smart Zoning and EIM

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 Green LED 3 s on / 1 s off

Show all 38 models

EL195UH040NE36B EL195UH060NE36B EL195UH080NE48C EL195UH100NE60C 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
E405	LSOM - compressor open circuit
E406	LSOM - open start circuit
E407	LSOM - open run circuit
E408	LSOM - welded contactor
E409	LSOM - low secondary voltage
F	Flame signal mode (button menu)
h	Heat pump stage (dual fuel)
H1	Gas heat, stage 1 (low fire)
H2	Gas heat, stage 2 (high fire)
LGWP Test button	Low GWP refrigerant detection board: modes and Test button
P	Program unit size (button menu)
Power-up size code	Unit size code shown at power-up (variable speed)

All Lennox Furnace error codes →

Lennox code Green LED 3 s on / 1 s off: homeowner questions

What does Lennox code Green LED 3 s on / 1 s off mean?

Soft disable - zoning damper module or EIM. On a Smart Zoning damper control module or an equipment interface module (EIM), the green LED blinks 3 seconds on and 1 second off. The thermostat found a device on the communication bus that it does not recognise and has parked it in…

Is it safe to keep using my furnace with code Green LED 3 s on / 1 s off?

Usually yes. Code Green LED 3 s on / 1 s off is normally minor, but if it keeps coming back have it checked.

Can I reset Lennox code Green LED 3 s on / 1 s off myself?

You can try one reset (power off for 30 seconds, then on). If Lennox code Green LED 3 s on / 1 s off comes back, the cause is still there and a licensed technician should check it.

Who can fix Lennox code Green LED 3 s on / 1 s off 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

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), 3. Soft Disable, p.7; Table 2 alert code 10, p.8. 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.