Lennox Error Code 40: HP heating lockout (Heat Pump)
Lennox error code 40 on a heat pump means: HP heating lockout. It is also called Lennox diagnostic code 40.
Homeowner? What Lennox code 40 means for you
Usually minor Your heat pump is reporting: HP heating lockout. 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 40 mean?
The heat pump could not raise room (or zone) temperature 0.5 F toward set point in 30 minutes, so it was locked out and the furnace / electric heat took over (dealer information). S30/S40 thermostat alert code 40.
Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems
Common causes of Lennox code 40
- Low airflow to the zone(s)
- Heat pump undersized for conditions or low charge
- Balance points set far apart
A technician checks these and 1 other possible causes on site before replacing any part.
Lennox models that use code 40
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 40: homeowner questions
What does Lennox code 40 mean?
HP heating lockout. The heat pump could not raise room (or zone) temperature 0.5 F toward set point in 30 minutes, so it was locked out and the furnace / electric heat took over (dealer information). S30/S40 thermostat alert code 40.
Is it safe to keep using my heat pump with code 40?
Usually yes. Code 40 is normally minor, but if it keeps coming back have it checked.
Can I reset Lennox code 40 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code 40 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code 40 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 Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.13. 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.