Model reference

Lennox G51MP-48C-090

Furnace

1 document10 error codes

Available documentation

Service Manual

G51MP Series Service Literature53 pg
Covers this model

MyPros+ Max

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M+

M+ Max·Lennox Furnace

LED1 ALTERNATING FAST FLASH / LED2 ALTERNATING FAST FLASH on my Lennox G51MP-48C-090

M+

Sensed during ignitor warm-up only:

From Service Manual 131532, p.24:

1.Access service mode to confirm the active fault code and read stored error history.

2.Measure control board supply voltage at test points. Expected: 12 VDC and 5 VDC.

3.Inspect all connectors on the main control for corrosion or backed-out pins.

Part WPW10804018

Electronic control board

Error codes (10)

CodeMeaning

LED1 ALTERNATING FAST FLASH / LED2 ALTERNATING FAST FLASHSensed during ignitor warm-up only LED1 ALTERNATING SLOW FLASH / LED2 ALTERNATING SLOW FLASHWatchguard LED1 FAST FLASH / LED2 FAST FLASH (simultaneous)Normal operation signaled when heating demand initiated at thermostat.LED1 FAST FLASH / LED2 SLOW FLASHMain power polarity reversed or improper main ground LED1 OFF / LED2 SLOW FLASHProve switch open, blocked inlet/exhaust vent, prove switch closed prior to…LED1 ON / LED2 ONCircuit board failure or control wired incorrectly LED1 ON / LED2 SLOW FLASHFlame sensed without gas valve energized, or rollout switch open, or low…LED1 SLOW FLASH / LED2 FAST FLASHLow flame signal LED1 SLOW FLASH / LED2 ONPrimary or secondary limit switch open; limit must close within 3 minutes or…LED1 SLOW FLASH / LED2 SLOW FLASH (simultaneous)Power on, normal operation; also signaled during cooling and continuous fan.

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