Model reference

Lennox G27M5(X)120

Furnace

1 document12 error codes

Available documentation

Service Manual

G27M Service Literature28 pg
Covers this model

MyPros+ Max

Diagnose your Lennox G27M5(X)120.

Step-by-step diagnostics from the service manual
Test values, resistance specs, and wiring references
Verified part numbers when replacement is needed

Start diagnosing

$29/month · Cancel anytime · Or $9.95 3-day pass

M+

M+ Max·Lennox Furnace

LED1-ALT_FAST_FLASH/LED2-ALT_FAST_FLASH on my Lennox G27M5(X)120

M+

Improper main ground or line voltage

From Service Manual 967052, 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 (12)

CodeMeaning

LED1-ALT_FAST_FLASH/LED2-ALT_FAST_FLASHImproper main ground or line voltage below 75 volts; OR broken ignitor; OR open…LED1-ALT_SLOW_FLASH/LED2-ALT_SLOW_FLASHWatchguard LED1-FAST_FLASH/LED2-FAST_FLASHNormal operation LED1-FAST_FLASH/LED2-SLOW_FLASHMain power polarity reversed LED1-OFF/LED2-ONCircuit board failure or control wired incorrectly.LED1-OFF/LED2-SLOW_FLASHPressure switch open or has opened 5 times during a single call for heat; OR…LED1-ON/LED2-ONCircuit board failure or control wired incorrectly.LED1-ON/LED2-SLOW_FLASHRollout switch open OR 9-pin connector improperly attached.LED1-SLOW_FLASH/LED2-FAST_FLASHLow flame signal LED1-SLOW_FLASH/LED2-OFFFlame sensed without gas valve energized.LED1-SLOW_FLASH/LED2-ONPrimary or secondary limit open. Units with board 63K8901 or 24L85 LED1-SLOW_FLASH/LED2-SLOW_FLASHPower on

Related Lennox furnace models

78,000+ service manuals · 160,000+ error codes · 55+ brands

$29/month · Cancel anytime · Or $9.95 3-day pass