Lennox Furnace Error Code 154 (E154): Refrigerant Leak Sensor #1 Lost Communication (Meaning, Causes, Fixes)
What the code means
Lennox's unit information for the SL280UHVK (R-454B) furnace lists E154 as "Refrigerant Leak Detector #1 Communication lost or invalid sensor dip switch configuration (Disable/Enable)". The same code appears in the EL180UHNEK, EL195UHNEK, SLP99UHVK and other K-series Lennox furnace literature. Lennox says there may be an issue with the wiring harness connecting sensor #1 to the furnace control board, either the wiring itself or the connector, or a damaged sensor or an obstruction at the harness plug. The code clears once communication with the sensor is re-established, but the blower stays on (latches) for at least 5 minutes, and you can re-test by pressing the Low GWP test button on the control board. E154 can also mean the Low GWP DIP switches are set wrong. Per Lennox's DIP switch table, one sensor on the SENSOR 1 plug is LGWP1 Enable / LGWP2 Disable, two sensors is Enable / Enable, and no sensor (R-410A or heat-only) is Disable / Disable. Disable / Enable is an invalid configuration. Both switches ship set to Enable, and Lennox warns that on furnace-only jobs or furnace replacements in non-A2L systems the sensors must be disabled, otherwise the blower will operate continuously. While a Low GWP fault is active, the blower runs at a constant airflow until the fault is cleared. Its sibling E155 is the same communication fault for sensor #2.
Likely causes
- Refrigerant sensor #1 cable not fully seated in the SENSOR 1 (LGWP1) plug on the furnace control board; Lennox says the Molex clip should lock in
- Damaged sensor wiring or connector, for example a cable pinched on sharp sheet metal or chafed where it runs to the evaporator coil
- Dust, debris or moisture in the sensor connection (Lennox calls for a drip loop below the board on upflow installs so condensate can't drip onto it)
- Low GWP DIP switches don't match the setup, for example still set to Enable on a furnace-only or R-410A system with no sensor installed, or set to the invalid Disable / Enable combination
- A damaged or failed refrigerant detection sensor that no longer talks to the board
Safe DIY checks
Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.
- Read the code carefully through the sight glass. E154 is a sensor communication problem; E150 means the sensor is actually reporting a refrigerant leak. If you see E150, or smell anything unusual, call a technician rather than troubleshooting yourself.
- Turn off power to the furnace at the service switch or breaker before opening the blower compartment door.
- Find the refrigerant sensor cable where it plugs into the control board at the plug marked LGWP1 (sensor #1). Check that it's pushed in until the clip locks, and look along the cable for cuts, pinches or a loose fit at the sensor end on the coil.
- If your furnace is heat-only, or is paired with an older R-410A air conditioner that has no refrigerant sensor, the most likely cause is the DIP switches. Lennox says both Low GWP switches must be set to Disable in that case. Only change them if you're sure no A2L system is connected, because Lennox warns that disabling refrigerant detection on an A2L system is prohibited by safety codes.
- Restore power. After the fix the blower will keep running for at least 5 minutes before the code clears. Pressing the Low GWP test button on the control board re-checks the fault, and if it's resolved the board returns to normal monitoring.
🛠 When to call a pro
- The furnace is connected to an R-454B or other A2L air conditioner or heat pump and the sensor cable looks fine; the sensor itself may need testing or replacement with a Lennox-approved part.
- E154 keeps coming back after the cable is reseated, or you see E150, E151, E155, E160 or E161 too.
- You aren't sure which DIP switch setting your system needs. Lennox requires an approved evaporator coil and sensor for Low GWP use, and the right setting depends on how many sensors were installed.
- The blower never shuts off even after the code clears.
Sources
- Lennox Unit Information 100176, SL280UHVK with R-454B: diagnostic code table (E150, E151, E152, E154, E155, E160, E161, E164), Section VII Low GWP application (LGWP1 plug, Molex clip, drip loop, DIP switch table, factory default Enable, furnace-only disable warning, Fault mode constant blower, LGWP test button functions) and maintenance step 15
- Lennox EL180UHNEK Series Unit Information, diagnostic codes table 4 (E154 definition, action required to clear and recover), ManualsLib copy
- Lennox EL195UHNEK Series Unit Information, diagnostic codes (E154), ManualsLib copy
Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.