Navien Error Code 003 (E003): Ignition Failure, Burner Won't Light (Meaning, Causes, Fixes)

What the code means

Navien's User's Information Manuals for the NPE and NPE-2 tankless water heaters and the NCB combi boilers all list E003 as Ignition failure, with the same first action: ensure that the main gas supply valve is open. According to the NCB-E service manual, the unit makes 10 ignition attempts, and if no flame is detected it shows 003E, which has to be cleared manually (Navien's UK combi manual also lists 003 as a manual-reset code). In plain terms, the burner didn't light, or it lit but the flame rod never sensed it. Don't confuse E003 with E012 (flame loss, meaning the flame lit and then went out) or E004 (false flame detection, meaning the unit sensed a flame when there shouldn't be one). Those codes share some parts but point to different problems.

Likely causes

• The main gas supply valve to the unit is closed, or gas service is off. This is the first thing all of Navien's user manuals list for E003.
• Gas supply pressure outside the operating range. Navien's NPE manuals specify 3.5 to 10.5 inches WC for natural gas and 8.0 to 13 inches WC for propane, measured at maximum firing rate.
• An empty or low propane tank on LP installations, which leaves the unit without enough gas to light
• A dirty, damaged or badly gapped igniter or flame rod. Navien's service manuals list an ignition gap of 3.5 to 4.5 mm (about 1/8 inch).
• A failed ignition transformer or gas valve, both listed in Navien's service manuals as parts that can cause E003
• Loose ground connection screws on the heat exchanger or a poorly grounded power cord. Navien's E003 checklist says to tighten the heat exchanger ground screws.
• Wrong DIP switch settings or the wrong gas orifice for the gas type, for example a natural gas unit hooked to propane without Navien's conversion kit
• Water collected in the flue or air intake on vertical vent installations, or a broken or clogged air pressure hose, both on the NCB service manual's checklist

Safe DIY checks

1. Check that the manual gas valve on the gas line going into the unit is open (the handle runs in line with the pipe).
2. Check that the rest of your gas is working: try a gas stove burner. On propane, check the tank gauge and refill if it's low.
3. Reset the unit: press Reset on the NPE front panel, or the Back button on NPE-2 models, as Navien's user manuals describe. For a combi boiler, reset from the front panel.
4. Open a hot water tap and see whether the unit lights. If E003 comes right back, don't keep resetting it over and over.
5. Look outside at the exhaust and intake vent terminations and clear away snow, leaves, nests or anything blocking them.
6. If you smell gas at any point, stop, leave the house, and call your gas company from outside. Don't flip switches or try to relight anything.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• E15 Bosch Dishwasher E15
• E24 Bosch Dishwasher E24
• E25 Bosch Dishwasher E25
• E18 Bosch Washer E18
• 24 Carrier Gas Furnace 24
• 33 Carrier Gas Furnace 33

All Navien codes →

Sources

1. Navien NPE User's Information Manual, Understanding Error Codes (E003 ignition failure: ensure the main gas supply valve is open; reset button)
2. Navien NPE-2 User's Information Manual, Understanding Error Codes (E003 ignition failure; reset with the Back button)
3. Navien NCB-E combi boiler User's Information Manual, Understanding Error Codes (E003 ignition failure)
4. Navien NPE service manual (E003 checklist: gas valve, gas pressure, orifice, dual venturi, DIP switches, heat exchanger ground screws; flame rod gap 3.5-4.5 mm; inlet gas pressure 3.5-10.5 in WC NG, 8.0-13 in WC LP, licensed professional only)
5. Navien NPE installation manual (gas supply pressure specs, rating plate, propane conversion kit required)
6. Navien NCB-240E service manual, 003 error occurrence conditions (10 ignition attempts, then 003E manually cleared; 13-item check list)
7. Navien UK NCB combi user manual (003 ignition failure, manual reset)