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21

Inverter Flash Code 21 (Red 2 flashes, Green 1 flash) — OD Inverter DC Peak Fault

Lennox · Communicating Systems

What does 21 mean?

The inverter has detected a DC peak fault. This can cause the outdoor unit to stop. If the peak current condition occurs 10 times within an hour, the system will lock out. The inverter LEDs will flash code 21 (Red: Two Flashes, Green: One Flash).

Common Causes

  • DC peak fault detected by inverter
  • High peak current detected

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Disconnect power to the outdoor control.

  2. 2

    Wait for 30 seconds.

  3. 3

    Reconnect power to the outdoor control to restart the system.

  4. 4

    If the issue persists, consult unit service documentation for detailed troubleshooting.

Browse all codes in this manual (41)
Verified technical data. Last updated: April 2026

Related Faults

14Inverter Flash Code 14 (Red 1 flash, Green 4 flashes) — OD Inverter Compressor Slowdown262 red flashes, 6 green flashes — Compressor startup fail292 red flashes, 9 green flashes — Compressor over-current
Source: Lennox Communicating Systems
Open Manual (Page 56)Search more codes in this manual