Lennox Error Code E420: EIM defrost out of cycle (Air Handler)
Lennox error code E420 on a air handler means: EIM defrost out of cycle. It is also called Lennox diagnostic code E420.
Homeowner? What Lennox code E420 means for you
Check, then call Your air handler is reporting: EIM defrost out of cycle. 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.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
- 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 E420 mean?
Defrost on the heat pump ran over 20 minutes (non-communicating heat pump paired with a communicating indoor unit). S30/S40 alert code 420; unit control shows E420.
Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems
Common causes of Lennox code E420
- Heat pump defrost control problem
- Low charge or coil sensor issue
Other Lennox Air Handler codes
| Code | Meaning |
|---|---|
| E354 | Electric heat stage 4 fault |
| E355 | Electric heat stage 5 fault |
| E371 | Float switch sensed open |
| E380 | EIM interlock relay fault |
| E381 | EIM interlock relay stuck |
| E382 | EIM relay W1 fault |
All Lennox Air Handler error codes →
Lennox code E420: homeowner questions
What does Lennox code E420 mean?
EIM defrost out of cycle. Defrost on the heat pump ran over 20 minutes (non-communicating heat pump paired with a communicating indoor unit). S30/S40 alert code 420; unit control shows E420.
Is it safe to keep using my air handler with code E420?
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 E420 myself?
You can try one reset (power off for 30 seconds, then on). If Lennox code E420 comes back, the cause is still there and a licensed technician should check it.
Who can fix Lennox code E420 near me?
Aurora Star Tech Inc. repairs Lennox air handlers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Troubleshooting guides
- Two horizontal lines on display (soft disable) - Lennox communicating Lennox · Air Handler
Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, 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.