Navien Error Code 109 (E109): Fan Motor Fault (Meaning, Causes, What to Do)

What the code means

Navien's NPE-2 and NPN User's Information Manuals both list E109 as "Abnormal operation: fan motor." According to the NPE service manual, the unit checks the fan's RPM signal after the fan starts. If the RPM stays low or near 0, or if a low or near-0 RPM signal is seen for 3 seconds while the burner is firing, the unit stops combustion, locks out the gas valve and ignition transformer, and shows 109E, which has to be cleared manually. In plain terms, the fan that pushes air through the burner isn't spinning the way the board expects. That's different from E110 (abnormal air pressure), where the fan runs but the air pressure sensor reads too little airflow, usually from a blocked vent, intake or condensate drain. The service manual groups E109 and E110 under the fan and lists its failure events as fan speed near 0 RPM, a loose fan mounting screw or a disassembled fan, and a disconnected or defective fan connection.

Likely causes

• A clogged intake air filter, the item on Navien's NPE-2 owner checklist and the first check in the service manual's E109 table
• A loose, disconnected or defective fan wire or connector, including the white connector that attaches the fan motor to the control board (PCB)
• A wet fan connector, for example from a leak inside the cabinet. Navien says to power the unit off and dry the parts completely before running it again.
• No or low power to the fan from the control board. Navien's manual gives a nominal fan supply range that a technician measures.
• A dirty fan, or a worn or failed fan motor that turns too slowly even with normal power
• A loose fan assembly screw or a fan that wasn't reassembled properly after service
• Less often, a faulty main control board (PCB), which Navien lists after the fan checks

Safe DIY checks

1. Clean the intake air filter. On NPE-2 models, Navien's steps are: turn the unit off, disconnect power, remove the front cover and the screw holding the filter (top left), pull the filter out, clean it with a toothbrush under running water, let it dry completely, reinstall it and the cover, then restore power and turn the unit on.
2. Look for any sign of water leaking inside the cabinet or onto the wiring. If you see it, leave the unit powered off and call for service, since Navien says wet fan connectors must be dried before the unit runs again.
3. If the display shows 109E, clear it from the front panel and run hot water once. If E109 comes back, stop resetting it and call for service.
4. Don't unplug or plug in the fan cable with the unit powered on. Navien warns this can damage the fan drive circuit or the main board.
5. If you smell gas at any point, leave the house and call your gas company from outside.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• E012 / 012 / 012E Navien Tankless Water Heater E012 / 012 / 012E
• 12 Rheem Tankless Water Heater 12
• 13 Rheem Tankless Water Heater 13
• 11 Rheem Tankless Water Heater 11
• 10 Rinnai Tankless Water Heater 10
• 11 Rinnai Tankless Water Heater 11

All Navien codes →

Sources

1. Navien NPE-2 User's Information Manual, Understanding Error Codes (E109 abnormal operation: fan motor, clean the intake air filter; E110 abnormal air pressure) and Cleaning the Air Intake Filter steps
2. Navien NPN User's Information Manual, Understanding Error Codes (E109 abnormal operation: fan motor, contact Technical Support)
3. Navien NPE Service Manual v2.21, section 5.1.9 109 Error (RPM checks, lock-out, 109E cleared manually, check items, fan action error table) and fan component failure events for E109/E110 (hosted copy)