Navien tankless water heater will not ignite; display shows E001 shortly after a hot water tap is opened.

Safety first: Turn OFF power to the water heater at the breaker and close the gas shutoff valve before removing covers. If you ever smell gas, stop immediately, ventilate the area, and contact your gas supplier or a licensed technician.

Step-by-step checks:

• 1. Reset the unit: Turn the unit OFF, wait 30 seconds, then turn it back ON. Open a hot water tap and see if the code reappears.
• 2. Verify gas supply: Ensure the manual gas shutoff valve near the Navien unit is fully open. Confirm other gas appliances in the home work normally. If multiple appliances fail, you may have a supply or regulator issue that requires a professional.
• 3. Inspect intake and exhaust: Check PVC or polypropylene vent pipes for obstructions (snow, leaves, bird nests, insect screens clogged). Make sure the intake air screen is clean and not blocked.
• 4. Clean the flame rod and burner area: With power and gas OFF, remove the front cover. Locate the flame rod (flame sensor) near the burner. Gently remove it and clean the metal probe with fine steel wool or a Scotch-Brite pad to remove oxidation. Reinstall securely. Visually inspect the burner surface for heavy dust or debris; vacuum gently if accessible.
• 5. Check wiring connections: Inspect the flame rod wiring harness and ignition transformer connections on the main PCB for loose or corroded terminals. Reseat connectors firmly.
• 6. Test operation: Restore gas and power, then run hot water. If E001 persists after cleaning and checks, the ignition transformer, flame rod, or gas valve may require replacement and gas pressure must be checked with a manometer by a qualified technician.

When to stop: If you are not comfortable working around gas or if the unit repeatedly fails to ignite after basic cleaning and vent checks, contact a Navien-authorized service technician.