Navien water heater shuts down with E002; burner lights briefly or not at all and then unit locks out.

Safety warning: Gas pressure diagnosis and adjustment should be performed only by a licensed gas technician with proper tools. Do not attempt to open or adjust the gas valve or regulator yourself.

User-level checks:

• 1. Confirm gas valves are open: Verify the manual gas shutoff at the heater and any upstream valves are fully open (handle parallel to the pipe).
• 2. Check other gas appliances: Turn on a stove or furnace. If they also fail or burn weakly, there may be a supply or meter issue that your gas utility must address.
• 3. Inspect gas line sizing (visual): If the Navien is far from the meter and fed by a small-diameter pipe (e.g., 1/2" over a long run), it may be undersized for the BTU rating. This requires a plumber to evaluate and possibly upsize the line.
• 4. Power reset: Turn the unit OFF, wait 30 seconds, then ON again. Open a hot water tap and see if the code returns.

Professional checks (do not DIY unless qualified):

• Measure inlet gas pressure at the Navien gas valve during operation.
• Inspect and clean the gas filter screen inside the gas valve assembly.
• Verify and adjust the gas regulator and combustion settings per Navien specifications.

If E002 persists after confirming valves are open and other appliances work normally, schedule service with a Navien-trained technician.