Navien Error Code E003

What the code is telling you

A tankless heater only fires when you open a hot tap. Water flow starts the sequence: the fan purges the burner, the igniter sparks, the gas valve opens and a sensor confirms flame. The code means that sequence ran and no flame was proven, so the unit locks out and you get cold water.

This is different from a heater that lights and then drops out partway through a shower. If you see other codes alongside this one, write them all down for the technician.

Common causes

The E003 entry in Navien's user manual names only the gas supply valve. The installation manual for the same heaters adds the conditions the burner needs to light, and each one is a likely cause when it isn't met:

• Gas valve closed. The first and most common thing to check.
• Gas pressure out of range. Navien's installation manual calls for 3.5 to 10.5 inches of water column on natural gas and 8.0 to 13 inches on propane. An undersized gas line or a bad regulator can drag pressure below that when the heater fires.
• Air in a new or repaired gas line. Navien's startup procedure purges the line by opening a hot water faucet so the heater runs and pushes gas through. After gas work, the first few tries can fail.
• Water reaching the ignition system. The installation manual warns that moisture can enter the unit and damage the ignition system.
• A blocked condensate line. Navien says not to cap or plug the condensate line, because condensate that can't drain can damage the water heater.
• Vent or intake problems. Navien tells owners to inspect the vent termination and air intake every year.

Safe checks you can do

1. Check the gas valve on the line into the heater. On a typical quarter-turn valve, the handle runs in line with the pipe when it's open.
2. Check that the house has gas. Light a stove burner or check another gas appliance. If nothing gas works, call the utility.
3. On propane, check the tank. A tank that ran dry also lets air into the lines, which means the line needs purging once it's refilled.
4. Look at the vent and intake outside. Snow, ice, leaves, a nest or a shrub can block them.
5. Look at the condensate drain line. It should run freely to a drain, with no kinks, ice or caps.
6. Reset and retry once. Navien's manual says to press the Back button to reset after an error. Then open a hot tap and see if the burner lights.

If the code comes straight back, stop resetting. Repeated ignition attempts on a heater with a real fault don't help, and they can hide the pattern a technician needs to see.

When to call a technician

Call if the gas is on, the vent is clear and the code keeps returning. Measuring gas pressure at the heater, checking the igniter and flame sensor, and opening the cabinet are jobs for a qualified technician. Navien's FAQ recommends contacting your original installer or a Navien Service Specialist for troubleshooting. Navien technical support is at 1-800-519-8794.

For budgeting, HomeGuide puts tankless water heater repairs at $300 to $1,300 on average. A tech will often flush the heat exchanger on the same visit if it's overdue; see how to flush a tankless water heater.

Which Navien models this covers

The meaning above comes from Navien's user manual for its NPE condensing water heaters, the line that includes the NPE-A2 and NPE-S2 series. Navien's combi-boilers and other product lines have their own manuals. If you own one of those, check the code table in your manual before you act on this page.

For more on keeping a tankless unit running, see our tankless water heater repair guide. If the repair quote is high and the unit is old, compare it with tankless water heater cost.