Lennox Error Code E427: Inverter DC peak fault (inverter code 21) (Heat Pump)
Lennox error code E427 on a heat pump means: Inverter DC peak fault (inverter code 21). It is also called Lennox diagnostic code E427.
Homeowner? What Lennox code E427 means for you
Call a technician Your heat pump is reporting: Inverter DC peak fault (inverter code 21). 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 E427 mean?
DC peak current of 55 A or higher detected; compressor and fan stop. 10 times in an hour = lockout. Inverter LED flash code 21 (red 2 flashes, green 1 flash). S30/S40 thermostat alert code 427 (shown as E427 on the unit control display).
Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems
Common causes of Lennox code E427
- Compressor current spike at restart
- Older inverter software (XP20/XP25 at defrost entry/exit)
Lennox models that use code E427
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 E427: homeowner questions
What does Lennox code E427 mean?
Inverter DC peak fault (inverter code 21). DC peak current of 55 A or higher detected; compressor and fan stop. 10 times in an hour = lockout. Inverter LED flash code 21 (red 2 flashes, green 1 flash). S30/S40 thermostat alert code 427 (shown as E427 on the unit control display).
Is it safe to keep using my heat pump with code E427?
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 E427 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code E427 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code E427 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.33. 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.