Boiler shuts down with E002 and does not fire, often after attempting ignition

Safety first: Turn off power before opening any panels. Allow the boiler to cool before bleeding air or opening any valves.

• Step 1 – Check system pressure: Look at the hydronic pressure gauge on the boiler or system. For most Navien boilers, cold pressure should be around 12–20 psi (consult your manual). If low, slowly add water via the fill valve/auto‑fill until within range. Do not over‑pressurize.
• Step 2 – Bleed air from system: Air pockets can prevent the flow sensor from detecting movement. Use manual air vents on radiators, baseboards, or air separators to purge air. Recheck and adjust system pressure afterward.
• Step 3 – Clean inlet water filter/strainer: Shut off isolation valves to the boiler. Remove the cold water inlet filter or system strainer (often a small mesh screen). Rinse debris under running water and reinstall.
• Step 4 – Inspect flow sensor: With power off and water isolated, locate the domestic or system flow sensor (turbine‑type sensor on the inlet piping). Check for scale or debris. Clean gently and ensure the rotor spins freely. Reassemble and check for leaks.
• Step 5 – Verify pump operation: Restore power and call for heat. Confirm the primary circulation pump runs and that supply and return pipes warm up. If the pump is not running, wiring or the pump itself may be faulty.

If E002 continues after restoring pressure and cleaning filters, the flow sensor or PCB may require replacement by a professional.