Lennox furnace Alert code 228: Inducer calibration issue
Alert 228 means the furnace control could not calibrate the pressure switch. The furnace performs a calibration routine, and this alert says it did not complete.
Applies to: Lennox communicating gas furnaces on systems using the S30, S40 or comparable communicating thermostats, as documented in the Lennox Residential Communicating Systems Alert Code Guide.
What it means
Lennox's communicating furnaces run a pressure switch calibration in which the control establishes the relationship between inducer speed and the pressure the switch sees. This alert means that routine failed. It is a distinctly modern fault — older furnaces simply had a switch with a fixed setpoint and no calibration step at all. The value of the calibration is that it lets the control adapt to a specific installation's venting; the cost is that anything disturbing the pressure signal prevents it completing. Lennox's checklist is the familiar one: vent blockage, inducer restriction, cold end heater box and drain, cracked hoses, and levelness.
Most common causes
- A vent blockage or restriction preventing a stable pressure reading.
- The combustion air inducer not operating correctly, or restricted.
- A blocked cold end heater box, condensate drain, or drain strainers.
- Cracked hoses in the pressure switch circuit.
- The unit not level.
- A pressure switch that has drifted out of its expected range.
How to diagnose it
- Check the outside vent termination for obstruction.
- Check the condensate drain for blockage or slow drainage.
- Note whether the furnace is level, since Lennox lists it among the checks.
- Note whether this appeared after installation or after service, since calibration runs at those points.
- Note that Lennox says this clears automatically after a successful calibration, so the alert going away means calibration succeeded rather than that a cause was found.
How to fix it
- Clear the vent termination and condensate drain if either is restricted. Both are homeowner-reachable.
- The inducer, pressure switch, hoses, and cold end heater box are technician work.
- If the unit is not level, correcting that properly matters for condensate drainage generally, not only for this alert.
- Lennox references Service and Application Note H-13-07 on condensing furnace pressure switch troubleshooting — worth a technician consulting.
Notes
Calibration-based pressure proving is more adaptive than a fixed switch and gives the control better information about the installation. It also means a furnace can fault for reasons that would not have troubled an older design, which is a real trade-off rather than a defect.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.