Lennox · Furnace

E164 Low GWP test mode active

Low severity Lennox ML180UHE

What the control is telling you

Shown when someone pressed the LGWP test button. Not a fault - normal operation resumes and the code clears by itself after 1 minute.

Applies to: ML180UHEK (R-454B era) single-stage 80% furnaces with integrated control 107792-XX (ML180UH045/070/090/110/135, incl. low-NOx X models)

Likely causes

LGWP test button pressed (manual test of leak mitigation)

Test and repair steps

Wait 1 minute for the test to end, or short-press the test button to end the test.
During the test the blower should run, the compressor/heat should shut off and the alarm relay should operate - use it to verify wiring after installation.
If the code shows without anyone pressing the button, check the button is not stuck.

Settings for these units

Filter sizes by cabinet width · Lennox ML180UHE

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Source: Lennox ML180UHEK Unit Information 100161/100166, Table 6 Integrated Diagnostic Codes, p.15; Tables 18-19, p.35. Summarized in our own words; check the original manual for your model.

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For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.