Lennox Error Code E402: System pressure trip (Heat Pump)
Lennox error code E402 on a heat pump means: System pressure trip. It is also called Lennox diagnostic code E402.
Homeowner? What Lennox code E402 means for you
Check, then call Your heat pump is reporting: System pressure trip. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
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 E402 mean?
Compressor overload, or suction or discharge pressure outside its limits. S30/S40 alert code 402; unit control shows E402.
Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems
Common causes of Lennox code E402
- High or low refrigerant charge
- Dirty coil or failed fan
- Restriction
Lennox models that use code E402
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 E402: homeowner questions
What does Lennox code E402 mean?
System pressure trip. Compressor overload, or suction or discharge pressure outside its limits. S30/S40 alert code 402; unit control shows E402.
Is it safe to keep using my heat pump with code E402?
It depends on the cause. This is often caused by something simple. Try the safe checks below; if the code returns, book a service call before it turns into a no-heat or no-hot-water emergency.
Can I reset Lennox code E402 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code E402 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code E402 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.29. 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.