Lennox Error Code LGWP Test button: Low GWP refrigerant detection board: modes and Test button (Furnace)

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

Lennox error code LGWP Test button on a furnace means: Low GWP refrigerant detection board: modes and Test button. It is also called Lennox diagnostic code LGWP Test button.

Low severityFurnaceLennox ML180UHE

Homeowner? What Lennox code LGWP Test button means for you

Usually minor Your furnace is reporting: Low GWP refrigerant detection board: modes and Test button. 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 LGWP Test button mean?

The ML180UHEK control has a Test/Reset button for the refrigerant leak (Low GWP) function. The board is always in one of four modes: Initializing (linking to the sensor and running a 5-minute purge), Normal (no leak detected), Leak Detected, or Fault. In Normal mode a press forces a simulated leak response, which shows code E164 for about a minute. In Leak Detected or Fault mode a press resets the board once the problem is fixed. A long press resets the control; a short press while initializing skips the rest of the pre-purge.

Applies to: Lennox ML180UHEK furnaces with Low GWP refrigerant detection control board

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 LGWP Test button

ML180UH045E36AK ML180UH045XE36AK ML180UH070E36AK ML180UH070E36BK ML180UH070XE36AK ML180UH070XE36BK ML180UH090E48BK ML180UH090E60CK ML180UH090XE48BK ML180UH110E60CK ML180UH110XE60CK ML180UH135E60DK

Other Lennox Furnace codes

Code	Meaning
E409	LSOM - low secondary voltage
F	Flame signal mode (button menu)
Green LED 3 s on / 1 s off	Soft disable - zoning damper module or EIM
h	Heat pump stage (dual fuel)
H1	Gas heat, stage 1 (low fire)
H2	Gas heat, stage 2 (high fire)
P	Program unit size (button menu)
Power-up size code	Unit size code shown at power-up (variable speed)
Red LED fast flash (heartbeat)	Call for heat - burner operation
Red LED off	No power to control or board fault
Red LED on steady	Board fault detected (107163-01)
Red LED recall button	Error recall button on the ignition control

All Lennox Furnace error codes →

Lennox code LGWP Test button: homeowner questions

What does Lennox code LGWP Test button mean?

Low GWP refrigerant detection board: modes and Test button. The ML180UHEK control has a Test/Reset button for the refrigerant leak (Low GWP) function. The board is always in one of four modes: Initializing (linking to the sensor and running a 5-minute purge), Normal (no leak detected), Leak…

Is it safe to keep using my furnace with code LGWP Test button?

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

Can I reset Lennox code LGWP Test button myself?

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

Who can fix Lennox code LGWP Test button 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 ML180UHEK 100166, Furnace Control Board Low GWP Modes of Operation and LGWP Test Button Functionality (Tables 18-19), printed p.34-35. 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.