Error code reference

Lennox Heat Pump Error Code Green FAST Flash / Red OFF

Discharge sensor lockout (5 strikes)

Discharge sensor lockout (5 strikes) — sensor out of range detected 5 times during a single Y1 demand; board locks out.

First step from the service manual

Cycle 24V power to board or short TEST pins 1-2 seconds to reset. Check/replace sensor harness.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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Green FAST Flash / Red OFF on my Lennox Heat Pump

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Discharge sensor lockout (5 strikes) — sensor

From Service Manual 709206, p.18:

1.Cycle 24V power to board or short TEST pins 1-2 seconds to reset. Check/replace sensor harness.

2.Measure door lock assembly resistance across the PTC terminals. Expected: ~200 ohms cold, rising sharply once energized.

3.Inspect strike and latch alignment. A warped door or misaligned strike prevents the switch stack from closing in the correct sequence.

Part W10810403

Door lock assembly

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