Navien Boiler Error Codes: E003, E110 and E302

By Ray Bennett · Updated 17 October 2026 · 7 min read · Checked against the sources at the end

Navien Boiler Error Codes: E003, E110 and E302

Short answer

Navien's NHB and original NFB boiler charts call E302 low water pressure. NCB-E and NCB-H combis instead list E351 for an automatic feeder fault. E003 means ignition failure across these four families; use the model's own chart for E110 and the reset button.

Navien boiler error codes tell you which check to start with, but the boiler family matters. Navien calls E302 low water pressure on its NHB and original NFB boilers; the NCB combi charts use E351 for a fault with the automatic water feeder.

This page covers NCB-E and NCB-H combis, NHB boilers and original NFB-175/NFB-200 boilers. It does not cover NPE tankless heaters, which have their own Navien tankless error code guide. NHB-H and NFB-H are also separate generations from the NHB and NFB manuals used here.

Before you start

What to carry: a torch, a phone or pen for the display, and your boiler’s model information. No cover removal is needed for the checks below.

Gas or electric? These Navien manuals cover gas boilers with electrical controls. An electric boiler needs its own maker’s chart.

Renting? Pass the fault and loss of heating or hot water to the person responsible for arranging repairs.

A gas smell or overheating comes before a reset.
Navien says to close the manual gas valve if the boiler overheats or its gas supply fails to shut off. Do not try to solve that situation by repeatedly restarting it. Navien’s NCB-E manual says to close the manual gas valve if the boiler is damaged by overheating, fire or flooding, and have a qualified technician inspect it before further use.

If you smell gas, Navien says not to light anything, operate electrical switches or use a phone in the building. Leave and call the gas supplier from outside. Follow their instructions, and call the fire department if the supplier cannot be reached.

If a carbon monoxide alarm sounds, CPSC says to leave for fresh air without looking for the source, call emergency services and count everyone to check that nobody is missing. Wait for permission before going back inside. If an appliance caused the alarm, CPSC says not to use it until trained personnel have serviced it.

Navien requires qualified installation and service. Keep electrical grounding repairs, gas settings, safety switch wiring and internal servicing with the repairer. Navien says not to use a boiler if any part has been under water. Call a qualified service technician immediately to inspect it and replace affected controls.

Find your Navien boiler manual

Check 1No parts or service tools for identification

Keep the letters in the model number

Record the full model, serial number and error, including any extra digits or words on the display. Navien asks for these details when arranging support. Also record whether the problem affects room heating, the hot taps or both.

The saved NCB-E manual covers NCB-150E, 180E, 210E and 240E. The NCB-H manual covers NCB-190/060H, 190/080H, 240/110H, 240/130H and 250/150H. The NHB manual covers NHB-055, 080, 110 and 150.

You can get the matching PDF from Navien’s official download pages for NCB-E, NCB-H, NHB or NFB. Choose the English User’s Information Manual for owner checks.

The letter after the model matters too. This example is an NHB boiler, not an NHB-H or an NCB combi.

E003 or 003: ignition failure

Check 2Supply information may settle the first check; recurring faults need diagnosis

Establish whether the gas supply was interrupted

Navien labels E003 ignition failure in all four manuals used here. On the NCB-E and NCB-H, its first listed action is to ensure the main gas supply valve is open.

A known utility interruption is worth reporting before anyone orders an ignition part. If a valve was closed for service or a safety concern, leave reopening it to the person handling that work. Do not bleed a gas line yourself.

Keep E012 separate: Navien calls it flame loss. For the two NCB families, its owner charts list intake air filter cleaning and proper electrical grounding. Those are checks for a specific code, not a reason to replace every part associated with ignition.

E110: air pressure or exhaust blockage

Check 3An outside look costs no parts; internal checks require servicing

Look for an outside obstruction without opening the vent

Navien calls NCB-E E110 abnormal air pressure, NCB-H E110 exhaust blockage, and NHB/NFB E110 exhaust vent closed. The NCB owner charts list an unobstructed exhaust pipe and a clean intake air filter as checks.

Look from the ground for anything covering an accessible outside termination, then report what you find. Do not climb to it, disconnect the vent or poke tools down the pipe. The number alone cannot confirm which obstruction or component is involved.

If filter cleaning is needed, use the complete procedure for that model or arrange it with the service visit. Leave the cabinet closed during the checks on this page.

E302, E351, E352 and E353 are different faults

Check 4A pressure reading first; valve, leak or sensor work depends on diagnosis

Read the heating water pressure before choosing a remedy

For the NHB and original NFB, Navien defines E302 as low water pressure. Report the visible pressure reading and any water leaking nearby. Do not assume a pressure sensor is faulty simply because the system reports low pressure.

For NCB-E and NCB-H, Navien’s E351 entry names the automatic feeder valve, which adds water to the heating circuit. Their owner charts direct that fault to technical support. E351 does not tell you that a particular valve must be replaced.

All four manuals distinguish E352 high water pressure from E353 water pressure sensor. The boiler pressure guide explains why the gauge reading is useful; the model’s own fill instructions must govern any correction.

Navien separates a water pressure condition from a feeder or sensor fault. The family labels are part of each meaning.

Other boiler codes worth separating

These selected entries come from Navien’s four owner manuals. A temperature sensor is also called a thermistor in the charts. Keep the family column with the code when passing it to the repairer.

Code	Models in this guide	What Navien identifies
E004	All four families	False flame detection
E016	All four families	Heat exchanger overheating
E030	NCB-E, NHB, NFB	Abnormal exhaust temperature
E030	NCB-H	Exhaust overheat
E109	All four families	Abnormal fan motor operation
E205 / E218	All four families	Heating supply / return temperature sensor fault
E271	NHB	Temperature differential limit
E291	NHB, NFB	Supply and return inversion limit
E407 / E421	NCB-E, NCB-H	Domestic hot outlet / cold inlet temperature sensor
E439	NCB-E	Abnormal flow sensor operation
E439	NCB-H	No domestic water flow detected
E480	Original NFB	Domestic hot water tank temperature sensor
E762 / E773	NCB-H	Vent pipe not fully inserted / improper gas type detected
E777	All four families	Low water cutoff fault or activation

Which button resets the boiler?

Check 5A button operation; unresolved faults need service time

Use the control's named reset, then check the affected service

Navien’s NCB-E and NHB manuals say to press Reset. The NCB-H and original NFB manuals use the Back button on the front panel. These instructions apply to ordinary troubleshooting after the safety conditions above have been ruled out.

The NHB and NFB tables also label some entries as alarms or automatic resets. That is how the control responds, not a finding that the boiler needs no repair.

If the suggested remedies and reset do not resolve the fault, Navien directs you to an authorised technician, licensed professional or technical support. After the boiler resumes operation, check the rooms or hot water that were affected and report any returning code.

What each one takes

Finding	Work to expect
NCB E003	Gas supply confirmation, followed by service diagnosis if it persists
NCB E110	Exhaust obstruction and intake filter checks
NHB or NFB E302	Low heating water pressure investigation
NCB E351	Automatic feeder troubleshooting through service support
E353	Water pressure sensor diagnosis
NCB-H E762 or E773	Qualified venting or fuel setup work

Questions people ask

Is E302 the code for low tap water pressure?

Navien lists it as low water pressure on the NHB and NFB boiler charts. Keep that boiler fault separate from a weak shower or faucet. Mention a weak tap separately when arranging the repair.

Does NCB-H E439 always mean a broken flow sensor?

Navien’s NCB-H owner manual calls it no domestic water flow detected. The older NCB-E chart uses different wording, abnormal flow sensor operation. Neither entry is a parts order by itself.

Should I bypass the low water cutoff for E777?

No. Navien identifies E777 with the low water cutoff and lists wiring and water level checks in the NCB charts. Leave that safety circuit to the repairer; do not bridge it to make the burner run.

Why are there hot water tank codes on the NFB list?

Navien’s original NFB chart includes E480 for the domestic hot water tank temperature sensor. That is a specific tank sensor entry, separate from the NCB combi’s domestic water flow codes.

What other details does Navien support need?

Along with the model, serial number and error, Navien asks for the purchase date, installation location and installation type.

The other boiler guides: boiler not working, boiler keeps turning off, and circulator pump problems.

Sources: Navien NCB-E User's Information Manual 20035566B, pp. 1, 3 to 5, 11, 22; NCB-H User's Information Manual, pp. 1, 3 to 5, 13, 25 to 26; NHB User's Information Manual 20032170C, pp. 1, 11, 22; original NFB User's Information Manual, English pp. 1, 10, 20; CPSC Carbon Monoxide Questions and Answers.