Lennox Error Code Green & Red alternating FAST flash: Coil (defrost) sensor problem (Heat Pump)
Lennox error code Green & Red alternating FAST flash on a heat pump means: Coil (defrost) sensor problem. It is also called Lennox diagnostic code Green & Red alternating FAST flash.
Homeowner? What Lennox code Green & Red alternating FAST flash means for you
Call a technician Your heat pump is reporting: Coil (defrost) sensor problem. The heat pump has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
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.
- Check both breakers and the outdoor disconnect box beside the outdoor unit; all should be ON.
- Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
- In winter, keep snow and ice off and away from the outdoor unit. A short defrost cycle with steam is normal.
- 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) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Lennox error code Green & Red alternating FAST flash mean?
The outdoor coil sensor reads open, shorted or out of range. The control will NOT run demand or time/temperature defrost, so the outdoor coil can ice up in heating; the system still heats and cools.
Applies to: Lennox EL16KP1 (Elite) and ML14KP1 (Merit) R-454B heat pumps, sizes -018 to -060, demand defrost control A108 (CMC1)
Common causes of Lennox code Green & Red alternating FAST flash
- Coil sensor open or shorted
- Coil sensor unplugged or loose at P4 (DIS-YEL)
- Sensor off its mounting location
A technician checks these and 1 other possible causes on site before replacing any part.
Lennox models that use code Green & Red alternating FAST flash
EL16KP1-018EL16KP1-024EL16KP1-030EL16KP1-036EL16KP1-042EL16KP1-048EL16KP1-060ML14KP1-018ML14KP1-024ML14KP1-030ML14KP1-036ML14KP1-042ML14KP1-048ML14KP1-060
Other Lennox Heat Pump codes
All Lennox Heat Pump error codes →
Lennox code Green & Red alternating FAST flash: homeowner questions
What does Lennox code Green & Red alternating FAST flash mean?
Coil (defrost) sensor problem. The outdoor coil sensor reads open, shorted or out of range. The control will NOT run demand or time/temperature defrost, so the outdoor coil can ice up in heating; the system still heats and cools.
Is it safe to keep using my heat pump with code Green & Red alternating FAST flash?
It depends on the cause. The heat pump has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Can I reset Lennox code Green & Red alternating FAST flash myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code Green & Red alternating FAST flash comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code Green & Red alternating FAST flash near me?
Aurora Star Tech Inc. repairs Lennox heat pumps in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: AC Running But Not Cooling: What to Check · Heat Pump Not Heating or Blowing Cold Air
Troubleshooting guides
- Heat pump not defrosting / outdoor coil iced - Lennox EL16KP1 / ML14KP1 Lennox · Heat Pump
- Low capacity or abnormal pressures - Lennox EL16KP1 / ML14KP1 Lennox · Heat Pump
- Outdoor unit will not start - Lennox EL16KP1 / ML14KP1 Lennox · Heat Pump
- Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Heat Pump
Source: Lennox EL16KP1 Unit Information 100195 / ML14KP1 Unit Information 100108, Table 4 Demand Defrost Control (A108) Diagnostic LEDs, p.32. 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.