Lennox Ducted Heating

Lennox Error Code ALTERNATING FAST FLASH

Ducted Heating:

What It Means

  • The following conditions are sensed Improper main ground (control board 32M88) during the ignitor warm-up period ONLY Improper main ground (control board 78M47 & 100973-01) continuously OR: Broken ignitor (control board 32M88) OR: Open ignitor circuit (control board 32M88) OR: Line voltage to control below Control board 32M88 75V Control board 78M47 & 100973-01 90V

Causes & actions from Lennox

How it shows
  • SureLight board LEDs (DS1/DS2): ALTERNATING FAST FLASH (led1: flashing (fast), led2: flashing (fast))
  • SureLight board LEDs (DS1/DS2): ALTERNATING FAST FLASH (led1: flashing (fast), led2: flashing (fast))
  • SureLight board LEDs (DS1/DS2): ALTERNATING FAST FLASH (led1: flashing (fast), led2: flashing (fast))

This manual entry does not list further causes or actions.

Applicable models & manual sources
  • G43UF

    The following conditions are sensed Improper main ground (control board 32M88) during the ignitor warm−up period ONLY Improper main ground (control board 78M47 & 100973−01) continuously OR: Broken ignitor (control board 32M88) OR: Open ignitor circuit (control board 32M88) OR: Line voltage to control below Control board 32M88 75V Control board 78M47 & 100973−01 90V

    G43UF manual, page 11

  • G43UF

    The following conditions are sensed Improper main ground (control board 32M88) during the ignitor warm−up period ONLY Improper main ground (control board 78M47 & 100973−01) continuously OR: Broken ignitor (control board 32M88) OR: Open ignitor circuit (control board 32M88) OR: Line voltage to control below Control board 32M88 75V Control board 78M47 & 100973−01 90V

    G43UF manual, page 11

  • G43UF

    The following conditions are sensed Improper main ground (control board 32M88) during the ignitor warm−up period ONLY Improper main ground (control board 78M47 & 100973−01) continuously OR: Broken ignitor (control board 32M88) OR: Open ignitor circuit (control board 32M88) OR: Line voltage to control below Control board 32M88 75V Control board 78M47 & 100973−01 90V

    G43UF manual, page 11

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

What should you check next?

Continue in ACLogics with guided diagnosis for your equipment and symptoms.

Download on the App Store Get it on Google Play
Scan to install on your phone Free · iPhone & Android
See how guided diagnosis works →