Model reference

Lennox G40UH-24A-070

Furnace

1 document11 error codes

Available documentation

Service Manual

G40UH Series Service Literature46 pg
Covers this model

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LED1 Alternating Fast Flash / LED2 Alternating Fast Flash on my Lennox G40UH-24A-070

M+

Improper main ground (controls 10M93,

From Service Manual 508186, p.38:

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 (11)

CodeMeaning

LED1 Alternating Fast Flash / LED2 Alternating Fast FlashImproper main ground (controls 10M93, 57L84 during ignitor warm up only…LED1 Alternating Slow Flash / LED2 Alternating Slow FlashWatchguard LED1 Fast Flash / LED2 Fast FlashNormal operation LED1 Fast Flash / LED2 Slow FlashMain power polarity reversed LED1 OFF / LED2 ONRollout switch open or 24V pin connector improperly attached.LED1 OFF / LED2 Slow FlashProve switch open, or blocked inlet/exhaust vent, or prove switch closed prior…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 24V pin…LED1 Slow Flash / LED2 Fast FlashLow flame signal LED1 Slow Flash / LED2 ONPrimary or secondary limit switch open LED1 Slow Flash / LED2 Slow FlashPower on, normal operation

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