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KB Home / Equipment / Gas Furnaces / Lennox/Ducane / G24M3 / G24M3 Diagnostic Codes/Fault Codes

G24M3 Diagnostic Codes/Fault Codes

Article ID: 750
Last updated: 11 Oct, 2024

Lennox Gas Furnace: G24M3

Re: Diagnostic Codes / Lockout Codes

There are 2 possible control boards on this furnace - a dual light board (Red & Green) and a single LED board.

ORIGINAL BOARD
Single-Light Furnace Control Board Fault Conditions

LED

 Description
Steady On Control Board Failure (Replace Control)
Slow Flash Normal Operation - No Call For Heat
Fast Flash Normal Operation - Call For Heat
2 Flashes Lockout - Failed to Sense or Sustain Flame
3 Flashes Pressure Switch Open
4 Flashes Open Limit
5 Flashes Flame Sensed with Gas Valve Off
REPLACEMENT CONTROL BOARD
Dual-Light Furnace Control Board Fault Conditions

DS1

(Red)

DS2

(Green)

 Description
Simultaneous Slow Flash Power On - No Call For Heat
Simultaneous Fast Flash Normal Operation - Call For Heat
Slow Flash On Primary or secondary limit switch open. Limit must close within 3 minutes or unit goes into
1−hour Watchguard.
Off Slow Flash Pressure Switch Fault: Open with inducer on or Closed with inducer off.
Alternating Slow Flash Watchguard −− Burners failed to ignite, limit open longer than 3 minutes, or flame sense lost 5
times in one heating cycle.
Slow Flash Off Flame sensed without gas valve energized.
On Slow Flash Rollout switch open.
On On

Control Board Failure or Control Mis-Wired.  Check 24V and 115V Wiring Connections.
Off On
On Off
Fast Flash Slow Flash Main power polarity reversed. Switch line and neutral. Improper main ground.
Slow Flash Fast Flash Low flame signal. Check flame sensor.
Alternating Fast Flash The following conditions are sensed during the ignitor warm−up period only:
1) Improper main ground;
2) Broken ignitor; OR: Open ignitor circuit;
3) Line voltage below 75 volts.
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Article ID: 750
Last updated: 11 Oct, 2024
Revision: 6
Access: Public
Views: 58
Comments: 0
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