HVACopediaLennox · Furnace
E155 Refrigerant leak sensor #2 communication lost
What the control is telling you
The control has lost communication with refrigerant detection sensor #2. The blower latches on for at least 5 minutes after communication returns.
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
- Damaged or unplugged sensor #2 harness or connector
- Sensor #2 damaged or plug obstructed
- LGWP2 enabled with no second sensor fitted
Test and repair steps
- Confirm whether a second sensor is required/installed; if not, set LGWP2 to Disable.
- Check the sensor #2 cable at the LGWP2 plug for proper seating, damage or moisture.
- Inspect the harness route (right side grommet) for cuts or pinches.
- Press the LGWP test button to retest the fault after repair.
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
- E150 A2L refrigerant leak alarm
- E151 A2L sensor fault
- E152 Refrigerant leak sensor #2 fault
- E154 Refrigerant leak sensor #1 communication lost / wrong DIP setting
- E160 Refrigerant leak sensor #1 wrong type
- E161 Refrigerant leak sensor #2 wrong type
- E163 Furnace control board failure
- E164 Low GWP test mode active
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Source: Lennox ML180UHEK Unit Information 100161/100166, Table 6 Integrated Diagnostic Codes, p.14; Table 17, p.33. 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.