Navien E003 Error Code: Ignition Failure

What you'll notice with E003

• No hot water at any fixture
• You hear the fan spin up, then the unit gives up after a few tries
• Code appears more often in the morning or when the furnace is running

What causes it

Gas supply off or undersized, low gas pressure, failed igniter, or blocked venting.

Safe steps you can take right now

1. 1Confirm the gas shutoff at the unit is fully open (handle parallel to the pipe).
2. 2Make sure other gas appliances still work — if nothing has gas, the problem is upstream.
3. 3Check that the vent terminations outside aren't blocked by leaves, nests, or a parked car.
4. 4Power the unit off for 30 seconds and back on. One reset only.

How we fix E003

If E003 returns, the most common San Jose cause is a gas line that can't hold pressure at the unit's full BTU draw — especially in homes where a tankless replaced a tank without upsizing the line. We measure dynamic gas pressure while the unit fires, then check the igniter, flame rod, and venting.

Verify gas pressure under load, inspect igniter and flame rod, check venting, replace failed components.