How to Fix / Troubleshooting

Safety: Components may be hot. Turn off power and allow the furnace to cool before working on it.

Steps to check:

Airflow checks: Replace the furnace filter, open all registers, and ensure return grilles are not blocked.
Blower speed settings: On variable-speed Daikin furnaces, verify that the blower speed tap or DIP switch settings are appropriate for the duct system (technician task).
Inspect discharge sensor: Confirm the discharge air thermistor is properly located in the supply plenum and not touching the heat exchanger or metal surfaces that could cause localized overheating.
Temperature rise: A technician should measure the temperature rise across the furnace and compare it to the rating plate. Excessive rise indicates airflow problems.

Persistent E3 faults require professional evaluation of duct design, blower performance, and sensor operation.

Daikin furnace shows E3; unit may shut down on high temperature or fail to complete a heating cycle.

Possible Causes