Safety: Use caution when working with line voltage. Turn off the breaker before opening electrical compartments.

Check breaker and switch: Verify that the furnace's dedicated circuit breaker is on and that any local service switch is in the ON position.
Inspect internal fuse: Remove the front cover and locate any line fuses on the PCB or power entry. Test with a multimeter and replace with the same type and rating if blown. Investigate the cause of the blown fuse.
Verify line voltage: With a multimeter and appropriate safety precautions, confirm that the correct voltage is present at the furnace's power terminals.
Check power connectors: Ensure that the power harness from the entry point to the PCB is fully seated and undamaged.
PCB replacement: If power is present but the display remains dead, the main PCB or display board may have failed and should be replaced by a qualified technician.

Navien furnace display is blank and the unit is completely unresponsive.

Possible Causes