Navien E003: Ignition Failure Causes and the Reset Steps by Family

Navien E003 means ignition failure: the unit tried to light and did not detect a flame. Confirm the main gas valve is open, then press Reset (NPE-A, NPE-S, NCB-E, NHB) or Back (NPE-A2, NPE-S2, NCB-H, NHB-H). If E003 returns, have inlet gas pressure measured at full fire.

What does E003 say on each Navien family, and what limits go with it?

E003 reads as ignition failure on all six Navien families we checked, but the reset button, the propane ceiling, the 2 in vent limit and the gas type switch all change by family. Pressures are in inches of water column (in W.C.), NG is natural gas, LP is propane, and vent limits are before elbow deductions.

Three things follow. An A2 or S2 owner hunting for a Reset button will not find it in the manual’s reset step, because that step is the Back button. A propane reading of 13.3 in W.C. passes on an NCB-E and fails on an NPE-A2. And a 70 ft run of 2 in vent fits only the A2 and S2 limit, so a replacement on an old vent path needs its numbers rechecked. An older NCB-180, NCB-210 or NCB-240 follows the NCB-E row for pressure, vent length and switch position, per its 2013 manual.

How do you reset Navien E003, and when do you stop resetting?

Reset E003 with the front panel button in the table above, after confirming gas is available, because five of the six charts name a gas check and a reset cannot open a closed valve. The NCB-180 service manual says the boiler attempts ignition 10 times before it shows 003E and waits to be cleared by hand.

1. If you smell gas, stop and leave the building. Do not touch switches or try to light anything. Per the NPE-A2 manual, call the gas supplier from a neighbor’s phone, or the fire department if you cannot reach them.
2. Find the manual shut-off on the gas line feeding the unit and confirm it is fully open. That is the first check in five of the six charts.
3. Confirm another gas appliance lights, or on propane, that the tank has fuel. A fault that hits 2 appliances points to supply, which belongs to the utility or propane supplier.
4. Press Reset (NPE-A, NPE-S, NCB-E, NHB) or Back (NPE-A2, NPE-S2, NCB-H, NHB-H) once. The NHB chart also accepts a power-on reset.
5. Open one hot tap fully and watch the display.
6. E003 back after 2 resets means stop. The manuals set no reset limit. That number is our editorial line, since a lockout can follow up to 10 tries of gas and spark.

On an NPE-A2 or S2, a tech can pull history the display does not show. Menu and Back held for 3 seconds opens the installer menu, and 1. Service Status Info items 5 to 9 count flame losses and 2nd, 3rd, 4th and 5th to 10th ignition attempts, per the 2026 installation manual. Past this point, the igniter, flame rod, gas valve and offset pressure are licensed gas work. If the display shows no code and there is still no hot water, our tankless water heater troubleshooting list starts from flow and power instead.

What should a manometer read at full fire on a Navien with E003?

A manometer should read 3.5 to 10.5 in W.C. on natural gas and at least 8.0 on propane, with the unit at its maximum firing rate, and every Navien manual we read assigns this test to a licensed pro. Pages that quote only 3.5 miss the ceiling: a natural gas line at 11 in W.C. is also out of range.

The NPE-A2 procedure runs 8 steps: close the gas shut-off, run a hot tap until the unit shuts down for lack of gas, shut the tap, remove the front cover, loosen the pressure port screw and zero the manometer, reopen the gas and leak check, open several high-flow fixtures, then read at maximum firing rate. A static reading skips that last step and cannot show a line that sags under load. Out-of-range readings go to the gas supplier or a qualified installer.

One half psi equals about 13.8 in W.C. (27.7 in W.C. per psi), above every ceiling in the chart, so a Navien on an elevated-pressure line needs a regulator ahead of it. The NCB-180 service manual states the propane case directly: low gas pressure on an LP model can cause ignition failure.

All six families use a 3/4 in NPT gas connection, which says nothing about the line behind it. Using the reference natural gas table in the NPE-A2 manual (0.5 in W.C. drop, supply under 6 in W.C., 1,000 BTU per cubic foot), a 199,900 BTU/H NPE-240A2 needs 199.9 cubic feet per hour. That table gives 3/4 in pipe 247 at 20 ft and 199 at 30 ft, so 3/4 in stops at 20 ft including fittings, before any other appliance is added. One inch pipe carries 207 at 90 ft. An NPE-150S2 at 150,000 BTU/H gets 50 ft on 3/4 in (151 cubic feet per hour), which is one reason to confirm what size tankless water heater the house needs before repiping. Check longer or shared runs against our gas pipe sizing chart. The same manual bars 1/2 in corrugated connectors, citing noise, and warns that crimps and tight bends in flex line restrict gas flow.

Could the wrong gas type or DIP switch setting cause E003?

Yes, a gas type mismatch belongs on the E003 list: the NPE-180A service manual names “proper dipswitch settings” and the “gas system and orifice” among its E003 checks, and the NCB-180 list asks whether the gas orifice plate matches the gas type. Navien units ship set for natural gas. Propane requires the conversion kit, the orifice change, the switch change and a gas/air ratio check by a qualified service agency, per the NPE-A2 and S2 propane conversion guide.

Moving the switch alone is not a conversion. Check the rating plate on the side of the unit against the gas on site first. The NPE-A2 manual warns that a different gas type causes abnormal combustion and malfunction, and says E773 flags a gas type mismatch but “may not detect all abnormal gas connections”, so a clean display does not clear the question. After a switch change on an A2 or S2, the panel shows error 788 until the installer runs the Gas Type Check. The NHB-H chart defines E788 as incorrect gas type setting. Power off before opening any switch cover.

How is E003 different from E012 and E110 on a Navien?

E003 means the burner never lit, E012 means it lit and lost flame, and E110 points at air or exhaust, and only E110 changes its printed wording by family. Match the family below before reading the code over the phone.

The owner charts do not put the condensate trap under E003, though online advice often does. The NHB-H chart puts it under E012, and the NPE-180A service manual lists the condensate drain pipe with its E110 exhaust blockage checks. The closest E003 tie is the NCB-180 list, which asks a tech to check for water collected in the flue and air supply on vertical vent runs. A trap never filled at install is still worth checking: the NPE-A2 manual says to fill it with water after installing the drain and never to cap the integrated condensate line.

Vent length works the same way. Vent limits line up with E110 and E012 before E003, and the arithmetic is tight. Each 90 degree elbow counts as 8 ft on 2 in pipe and 5 ft on 3 in. Six 90s on a 60 ft NCB-E 2 in run use 48 ft and leave 12 ft of straight pipe. The same six on an NPE-A2 leave 27 ft. On NPE models a concentric termination takes off 5 ft more. Our water heater venting requirements page covers material and clearances.

Which readings will a Navien tech or support line ask for on E003?

Navien’s support line at 1-800-519-8794 asks for model number, serial number, purchase date, installation location and type, and the error code, per the NCB-E manual. The other rows support the checks above. Fill this in before the call, and ask for an inlet gas pressure test at maximum firing rate by name.