Lennox Error Code Green SLOW flash / Red ON: Discharge line temperature fault (Heat Pump)
Lennox error code Green SLOW flash / Red ON on a heat pump means: Discharge line temperature fault. It is also called Lennox diagnostic code Green SLOW flash / Red ON.
Homeowner? What Lennox code Green SLOW flash / Red ON means for you
Usually minor Your heat pump is reporting: Discharge line temperature fault. This code is usually informational or minor. The safe checks below often clear it; call us if it keeps showing up.
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 SLOW flash / Red ON mean?
Should not occur on these units: no discharge sensor is used, a 10K resistor sits on the discharge sensor terminals (COIL-BROWN). A shorted resistor makes the control see high discharge temperature. (The table text says ML14KP1 even in the EL16KP1 manual.)
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 SLOW flash / Red ON
- Shorted 10K resistor on the discharge sensor connection
- Wiring short at the discharge sensor terminals
Lennox models that use code Green SLOW flash / Red ON
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 SLOW flash / Red ON: homeowner questions
What does Lennox code Green SLOW flash / Red ON mean?
Discharge line temperature fault. Should not occur on these units: no discharge sensor is used, a 10K resistor sits on the discharge sensor terminals (COIL-BROWN). A shorted resistor makes the control see high discharge temperature. (The table text says ML14KP1 even in…
Is it safe to keep using my heat pump with code Green SLOW flash / Red ON?
Usually yes. Code Green SLOW flash / Red ON is normally minor, but if it keeps coming back have it checked.
Can I reset Lennox code Green SLOW flash / Red ON myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code Green SLOW flash / Red ON comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code Green SLOW flash / Red ON 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.