Fault Code Lookup

HVAC Sales Master

E390

Low GWP relay stuck

This code typically points to

Furnace control low-GWP relay fault

Next checks to confirm

Verify relay operation
Replace indoor unit control board if relay fault persists

Escalation

Board-level low-GWP hardware fault

Reset behavior

Clears when relay operates normally.

Safety Critical

Immediate concern

⚠ Cross-generation conflict

Codes E150, E151, E152, E154, E155, E160, E161, E163, E164, and E390 only exist on K-revision Lennox furnaces (EL195UHNEK, ML196UHEK). These are refrigerant leak detection codes for R-454B A2L compliance. E154/E155 will latch the blower ON for at least 5 minutes regardless of thermostat call — this is a code-mandated safety behavior. A2L refrigerant detection CANNOT be disabled — it's prohibited by safety codes.

Source

Lennox EL195UHNEK Installation Instructions 508575-01, p.47

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