Boiler shows E018 and will not operate, often after a power event

Safety first: Turn off power at the breaker before tightening any electrical connections. Only qualified persons should work inside electrical compartments.

• Step 1 – Check breaker and circuit: Ensure the boiler is on a dedicated circuit of the correct amperage. Reset the breaker if tripped.
• Step 2 – Measure voltage: Have a qualified person measure line voltage at the boiler terminals. Compare to Navien specifications (typically 120 VAC in North America). Low or fluctuating voltage can trigger E018.
• Step 3 – Inspect internal connections: With power off, check that all screw terminals and plug connectors on the power supply and PCB are tight and fully seated.
• Step 4 – Surge protection: If E018 occurred after a storm or surge, the internal power supply or PCB may be damaged and require replacement.

Do not bypass safety devices or operate the boiler on an undersized or unstable electrical supply.