Lennox Ducted Heating

Lennox Error Code Fast flash

Ducted Heating

Fast flash means different things on different Ducted Heating models. Enter your model number to see only your reading, or find your model below.

What It Means

  • G24M: After combustion blower starts: pressure CLOSED? NO: check main valve OFF; hold until switch CLOSES; fast flash. Ignition trial7seconds after45second prepurge: flame not registered, valve and spark OFF, increment trial register; three completed trials give ignition reset, combustion/system fans OFF, wait60minutes; fast flash. During running flame loss, start spark within0.8seconds maximum, test recovery within7seconds; failure turns valve/spark OFF and retries. After run limit/pressure switch closes combustion fan ON, system fan OFF after selected delay; fast flash. Parenthetical holding/reset is extraction annotation, not a lamp code.
  • G24M: Thermostat calls for heat; normal heating sequence begins. Fast flash alone also occurs on the separate pressure-hold and ignition-reset branches; operating stage matters.

Causes & actions from Lennox

After combustion blower starts: pressure CLOSED? NO: check main valve OFF; hold until switch CLOSES; fast flash. Ignition trial7seconds after45second prepurge: flame not registered, valve and spark OFF, increment trial register; three completed trials give ignition reset, combustion/system fans OFF, wait60minutes; fast flash. During running flame loss, start spark within0.8seconds maximum, test recovery within7seconds; failure turns valve/spark OFF and retries. After run limit/pressure switch closes combustion fan ON, system fan OFF after selected delay; fast flash. Parenthetical holding/reset is extraction annotation, not a lamp code.

Models: G24M

How it shows
  • ram diagnostic led: Fast flash

Sequence holding while waiting for pressure switch to close, or in 60-minute ignition reset period following three unsuccessful ignition trials.

Applicable models & manual sources
  • G24M

    After combustion blower starts: pressure CLOSED? NO: check main valve OFF; hold until switch CLOSES; fast flash. Ignition trial7seconds after45second prepurge: flame not registered, valve and spark OFF, increment trial register; three completed trials give ignition reset, combustion/system fans OFF, wait60minutes; fast flash. During running flame loss, start spark within0.8seconds maximum, test recovery within7seconds; failure turns valve/spark OFF and retries. After run limit/pressure switch closes combustion fan ON, system fan OFF after selected delay; fast flash. Parenthetical holding/reset is extraction annotation, not a lamp code.

    G24M manual, page 24

Thermostat calls for heat; normal heating sequence begins. Fast flash alone also occurs on the separate pressure-hold and ignition-reset branches; operating stage matters.

Models: G24M

How it shows
  • ram diagnostic led: Fast flash

Thermostat calls for heat (normal sequence initiated / call for heat active).

Applicable models & manual sources
  • G24M

    Thermostat calls for heat; normal heating sequence begins. Fast flash alone also occurs on the separate pressure-hold and ignition-reset branches; operating stage matters.

    G24M manual, page 24

Disclaimer: This information is for general reference. Code wording and instructions vary by model. Always follow the service manual for your exact unit.

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