Error code reference
Lennox Heat Pump Error Code Green FAST Flash / Red ON
Discharge line temperature lockout (5 strikes)
Discharge line temperature lockout (5 strikes) — discharge line temperature fault occurred 5 times during a single Y1 demand; detects shorted sensor or high discharge temperatures.
First step from the service manual
Cycle 24V power to board or short TEST pins 1-2 seconds to reset. Check discharge sensor and system operation.
The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.
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Get the full diagnostic procedure for Green FAST Flash / Red ON.
- Step-by-step tests with expected resistance, voltage, and continuity values
- Wiring diagram references and connector pinouts from the OEM service manual
- Verified part numbers when replacement is required
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