Lennox Ducted Heating

Lennox Error Code 3 flashes

Ducted Heating:

What It Means

  • Before combustion blower starts: pressure OPEN? NO: check main valve OFF; hold until pressure switch OPENS. During operation pressure CLOSED? NO: main valve OFF, combustion/system fans ON; hold until switch CLOSES. The initial failed-close branch is FAST flash, not3flashes.

Causes & actions from Lennox

How it shows
  • ram diagnostic led: 3 flashes

Pressure switch failed open or failed closed (pressure switch open prior to start or failing to close / opening during operation).

Applicable models & manual sources
  • G24M

    Before combustion blower starts: pressure OPEN? NO: check main valve OFF; hold until pressure switch OPENS. During operation pressure CLOSED? NO: main valve OFF, combustion/system fans ON; hold until switch CLOSES. The initial failed-close branch is FAST flash, not3flashes.

    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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