HVACopediaLennox · Furnace
E164 Low GWP test mode active
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
| Cabinet | Side return | Bottom return |
|---|---|---|
| A - 14-1/2 in. | 16 x 25 x 1 (1) | 14 x 25 x 1 (1) |
| B - 17-1/2 in. | 16 x 25 x 1 (1) | 16 x 25 x 1 (1) |
| C - 21 in. | 16 x 25 x 1 (1) | 20 x 25 x 1 (1) |
| D - 24-1/2 in. | 16 x 25 x 1 (2) | 24 x 25 x 1 (1) |
Filters are field supplied; check monthly.
Cabinet letter is the letter after the cooling size in the model number: A = 045E36AK, 070E36AK; B = 070E36BK, 090E48BK; C = 090E60CK, 110E60CK; D = 135E60DK.
Models that show this code
12 models in Lennox ML180UHE
Other codes on the same units
- E152 Refrigerant leak sensor #2 fault
- E154 Refrigerant leak sensor #1 communication lost / wrong DIP setting
- E155 Refrigerant leak sensor #2 communication lost
- E160 Refrigerant leak sensor #1 wrong type
- E161 Refrigerant leak sensor #2 wrong type
- E163 Furnace control board failure
- E200 Flame rollout - hard lockout
- E204 Gas valve miswired
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
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.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.