Navien boiler error codes (combi and heating-only boilers)

Navien boiler error code E001: heat exchanger overheat

Checked October 2026

Short answer E001 on a Navien boiler means heat exchanger overheat (NFB, NHB, NFB-C and NFB700-C tables: 'over temperature'). The NCB-H manual says to reset it once from the front panel; if it comes back, call an authorized technician or Navien Technical Support. See what to check

What it means

E001 is Navien’s heat exchanger overheat code. The NCB-H, NCB700, NFC-H, NFB-H and NHB-H tables word it “Heat Exchanger Overheat” (navien-ncb-h-um-2501, p. 25; navien-ncb700-io, p. 136; navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). The NFB, NHB, NFB-C and NFB700-C tables say “Heat exchanger over temperature” (navien-nfb-um, p. 20; navien-nhb-um, p. 22; navien-nfb-c-um, p. 19; navien-nfb700-c-io, p. 119). The tables say nothing more about the condition. The NCB-E table has no E001 (navien-ncb-e-um, p. 22).

Do not mix it up with E016. In the NCB-H and NCB700 tables, E016 has the same words, “Heat Exchanger Overheat”, with different actions: turn off the system for at least 30 minutes and then restart it, and flush the heat exchanger (navien-ncb-h-um-2501, p. 25; navien-ncb700-io, p. 136). The NFC-H, NFB-H and NHB-H user’s manuals also use the same words for both codes (navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). The manuals do not explain how the two codes differ, so go by the number on the display.

Check these first

For E001 the NCB-H user’s manual gives one action, “Reset the boiler from the front panel.” (navien-ncb-h-um-2501, p. 25). The NCB700 and NFC installation manuals give the same one (navien-ncb700-io, p. 136; navien-nfc-io, p. 101).

1. Reset the boiler once: on the NCB-H, press Back on the front panel (navien-ncb-h-um-2501, p. 13). The NCB700 and NFC installation manuals also name the Back button (navien-ncb700-io, p. 116; navien-nfc-io, p. 87).
2. If E001 comes back after the reset, the manual’s next step is an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 24).
3. When you call, have the model number, serial number, date purchased, installation location and type, and the error code ready (navien-ncb-h-um-2501, p. 64).

On the NFC-H, NFB-H and NHB-H, the E001 row reads “Check for proper system flow.” (navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). The manuals do not say who checks the flow or how, and they give the owner no procedure for it. The reset on these three is the Back button (navien-nfc-h-um-c, p. 13; navien-nfb-h-um, p. 13; navien-nhb-h-um, p. 14).

When to call a licensed technician

• E001 returns after one reset (navien-ncb-h-um-2501, p. 24).
• The system flow check from the NFC-H, NFB-H and NHB-H tables (navien-nfb-h-um, p. 23).
• Anything inside the boiler. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-ncb-h-um-2501, p. 5).
• The seasonal inspection. A qualified technician should inspect the boiler at the beginning of every heating season and when there is a problem (navien-ncb-h-um-2501, p. 18).

Related codes: E016, E046, E030. All Navien boilers codes

Navien boiler error code E003: ignition failure, what to check

Checked October 2026

Short answer On Navien boilers, E003 means ignition failure. If you smell gas, follow the gas safety steps on this page. On the NCB-H and NCB-E, check that the main gas supply valve is open and reset once; if E003 returns, call an authorized technician. See what to check

What it means

E003 is Navien’s ignition failure code. Every Navien boiler table used here has it, from the NCB-H combi to the NFB700-C, worded “Ignition Failure” or “Ignition failure” (navien-ncb-h-um-2501, p. 25; navien-nfb-um, p. 20; navien-nfb700-c-io, p. 119). These boilers have no pilot: an ignition device lights the burner automatically, and the user’s manual says not to try to light the burner by hand (navien-ncb-h-um-2501, p. 3).

The code tables do not say what stopped the ignition. A one-page Navien parts guide for the NCB-H says ignition failure can occur when there is a buildup of dirt or white powder (navien-ncb-h-emergency-kit, p. 1).

Check these first

The NCB-H user’s manual gives one action for E003 (navien-ncb-h-um-2501, p. 25), and the NCB-E manual gives the same one (navien-ncb-e-um, p. 22).

1. If you smell gas, stop and follow the steps at the top of this page. Before operating the boiler, the manual says to smell all around the appliance area for gas, next to the floor as well, because some gas is heavier than air (navien-ncb-h-um-2501, p. 3).
2. Make sure the main gas supply valve is open (navien-ncb-h-um-2501, p. 25).
3. Reset the boiler once. On the NCB-H press Back on the front panel (navien-ncb-h-um-2501, p. 13); on the NCB-E press Reset (navien-ncb-e-um, p. 11).
4. If E003 comes back, the manual’s next step is an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 24). Have the model number, serial number, date purchased, installation location and type, and the error code ready (navien-ncb-h-um-2501, p. 64).

The NFC-H, NFB-H and NHB-H user’s manuals word the E003 check as “Check gas supply valve and igniter.” and do not say who does it (navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). They give the owner no procedure for the igniter, and they tell owners not to repair or replace any part of the boiler unless the manual specifically recommends it (navien-nfb-h-um, p. 5). The reset on these three is the Back button (navien-nfc-h-um-c, p. 13; navien-nfb-h-um, p. 13; navien-nhb-h-um, p. 14).

When to call a licensed technician

• E003 returns after the gas valve check and one reset (navien-ncb-h-um-2501, p. 24).
• Ignition failure that keeps happening on an NCB-H. Navien’s Emergency Kit Quick Guide describes a flame rod service for it. That work includes removing the igniter and fitting a new igniter gasket, and the guide warns that using the old gasket can cause gas leakage, which can cause severe personal injury or death (navien-ncb-h-emergency-kit, p. 1). The user’s manual has no igniter procedure for the owner and tells owners not to repair or replace any part unless it specifically recommends it (navien-ncb-h-um-2501, p. 5).
• Anything on the gas supply past the valve. The user’s manual cover says installation and service must be performed by a qualified installer, service agency or the gas supplier (navien-ncb-h-um-2501, p. 1).

Related codes: E012, E004, E020. All Navien boilers codes

Navien boiler error code E012: flame loss, what to check

Checked October 2026

Short answer On Navien boilers, E012 means flame loss. On the NCB-H and NCB-E the manual's steps are to clean the intake air filter with the power off and make sure the cord is properly grounded; if E012 returns after one reset, call an authorized technician. See what to check

What it means

E012 is Navien’s flame loss code. Every Navien boiler table used here has it, worded “Flame Loss” or “Flame loss” (navien-ncb-h-um-2501, p. 25; navien-nfb-um, p. 20; navien-nfb700-c-io, p. 119). The tables say nothing more about the condition, and the action that goes with it depends on the series.

Check these first

The NCB-H user’s manual gives two actions for E012: “Clean the intake air filter.” and “Ensure that the electrical cord is properly grounded.” (navien-ncb-h-um-2501, p. 25). The NCB-E manual gives the same two (navien-ncb-e-um, p. 22).

1. Clean the intake air filter (navien-ncb-h-um-2501, p. 25). The procedure starts with the power off: press the Power button to turn the boiler off and disconnect its power supply before you unfasten the four latches and remove the front cover. The filter is at the top left, held by one screw; dust and rinse it under clean running water, let it dry completely, refit it and the cover, then reconnect the power (navien-ncb-h-um-2501, pp. 16–17). The E110 page lists the steps in full.
2. Make sure the boiler’s electrical cord is properly grounded (navien-ncb-h-um-2501, p. 25). The manual does not say how to check this. Among its service options it lists a licensed professional for the affected system, for example an electrician (navien-ncb-h-um-2501, p. 64).
3. Reset the boiler once. On the NCB-H press Back on the front panel (navien-ncb-h-um-2501, p. 13); on the NCB-E press Reset (navien-ncb-e-um, p. 11).
4. If E012 comes back, the manual’s next step is an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 24).

On the NCB-E the filter procedure is different: three buckles hold the cover, and the filter is cleaned with a toothbrush and clean running water (navien-ncb-e-um, pp. 14–15).

On the NFC-H, NFB-H and NHB-H the E012 row reads “Check gas, venting and condensate trap.” and does not say who checks (navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). The owner maintenance schedule in the same manuals is not tied to any code, but it does give the owner two related monthly items: a visual inspection of the vent piping for signs of leakage and blockage, and an inspection of the condensate trap and the PVC fittings (navien-nfc-h-um-c, p. 18; navien-nfb-h-um, p. 17; navien-nhb-h-um, p. 18). Cleaning the condensate trap is in the service technician’s section of those manuals (navien-nfc-h-um-c, p. 19; navien-nfb-h-um, p. 18; navien-nhb-h-um, p. 19).

When to call a licensed technician

• E012 returns after the filter, the cord check and one reset (navien-ncb-h-um-2501, p. 24).
• Anything on the gas supply. The user’s manual cover says installation and service must be performed by a qualified installer, service agency or the gas supplier (navien-ncb-h-um-2501, p. 1).
• Cleaning the condensate trap, which the manuals place in the service technician’s section (navien-nfb-h-um, p. 18).
• Anything inside the boiler beyond the air filter. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-ncb-h-um-2501, p. 5).

Related codes: E003, E004, E110. All Navien boilers codes

Navien boiler error code E109: abnormal fan motor

Checked October 2026

Short answer On Navien boilers, E109 is 'abnormal fan motor'. On the NCB-H and NCB-E the one owner step is to clean the intake air filter with the power off; if E109 returns after one reset, call an authorized technician or Navien Technical Support. See what to check

What it means

E109 is Navien’s fan motor code. The NCB-H, NCB700, NFC-H, NFB-H and NHB-H tables call it “Abnormal Fan Motor” (navien-ncb-h-um-2501, p. 25; navien-ncb700-io, p. 136; navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). The NCB-E, NFC, NFB, NHB, NFB-C and NFB700-C tables say “Abnormal operation: fan motor” (navien-ncb-e-um, p. 22; navien-nfc-io, p. 101; navien-nfb-um, p. 20; navien-nhb-um, p. 22; navien-nfb-c-um, p. 19; navien-nfb700-c-io, p. 119). The tables do not describe the fault further.

Check these first

The NCB-H user’s manual gives one action for E109, “Clean the intake air filter.” (navien-ncb-h-um-2501, p. 25). The NCB-E manual gives the same one (navien-ncb-e-um, p. 22), and so do the NCB700 and NFC installation manuals (navien-ncb700-io, p. 136; navien-nfc-io, p. 101).

1. Clean the intake air filter (navien-ncb-h-um-2501, p. 25). The procedure starts with the power off: press the Power button to turn the boiler off and disconnect its power supply before you unfasten the four latches and remove the front cover. The filter is at the top left, held by one screw; dust and rinse it under clean running water, let it dry completely, refit it and the cover, then reconnect the power (navien-ncb-h-um-2501, pp. 16–17). The E110 page lists the steps in full. On the NCB-E, three buckles hold the cover and the filter is cleaned with a toothbrush and clean running water (navien-ncb-e-um, pp. 14–15).
2. Reset the boiler once. On the NCB-H press Back on the front panel (navien-ncb-h-um-2501, p. 13); on the NCB-E press Reset (navien-ncb-e-um, p. 11).
3. If E109 comes back, the manual’s next step is an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 24). Have the model number, serial number, date purchased, installation location and type, and the error code ready (navien-ncb-h-um-2501, p. 64).

On the NFC-H, NFB-H and NHB-H the E109 row reads “Check fan and venting.” and does not say who checks (navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). These manuals give the owner no procedure for the fan, and they tell owners not to repair or replace any part unless the manual specifically recommends it (navien-nfb-h-um, p. 5). The owner maintenance schedule, which is not tied to any code, includes a monthly visual inspection of the vent piping for signs of leakage and blockage (navien-nfb-h-um, p. 17). The reset on these three is the Back button (navien-nfc-h-um-c, p. 13; navien-nfb-h-um, p. 13; navien-nhb-h-um, p. 14).

When to call a licensed technician

• E109 returns after a clean filter and one reset (navien-ncb-h-um-2501, p. 24).
• The fan check from the NFC-H, NFB-H and NHB-H tables (navien-nfb-h-um, p. 23).
• A vent or intake pipe that is damaged, separated at a joint, or shows corrosion, rusting or melting. Turn the boiler off and stop using it (navien-ncb-h-um-2501, p. 4).
• Anything inside the boiler beyond the air filter. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-ncb-h-um-2501, p. 5).

Related codes: E110, E123, E012. All Navien boilers codes

Navien boiler error code E110: exhaust blockage, what to check

Checked October 2026

Short answer On Navien NCB-H, NFC-H, NFB-H and NHB-H boilers, E110 is 'exhaust blockage'; other series word it differently, see the table below. Make sure the exhaust pipe is clear and clean the intake air filter with the power off; if it returns, call a technician. See what to check

What it means

On the NCB-H, NCB700, NFC-H, NFB-H and NHB-H, E110 is “Exhaust Blockage” (navien-ncb-h-um-2501, p. 25; navien-ncb700-io, p. 136; navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). Other tables word it differently; see the notes at the end of this page.

The user’s manuals also name a cause on the intake side. If the air intake filter becomes clogged by dust or lint, the boiler stops operating and “Error Code 110” appears on the front panel display (navien-ncb-h-um-2501, p. 16). The NFC-H, NFB-H, NHB-H, NCB-E, NFB and NHB user’s manuals say the same (navien-nfc-h-um-c, p. 15; navien-nfb-h-um, p. 15; navien-nhb-h-um, p. 16; navien-ncb-e-um, p. 14; navien-nfb-um, p. 12; navien-nhb-um, p. 13).

Check these first

These steps follow the NCB-H user’s manual, whose E110 row gives two actions (navien-ncb-h-um-2501, p. 25). The NCB-E row gives the same two (navien-ncb-e-um, p. 22); its filter procedure is in the notes below.

1. Make sure the exhaust pipe is free of obstructions (navien-ncb-h-um-2501, p. 25). The manual does not say how to check. Its owner maintenance schedule describes the monthly vent check as a visual inspection of the vent piping for signs of leakage and blockage (navien-ncb-h-um-2501, p. 18).
2. While you look, check the pipes for damage. If any vent pipe, vent elbow or intake pipe is damaged, separated at a joint, or shows corrosion, rusting or melting, turn the boiler off and stop using it (navien-ncb-h-um-2501, p. 4).
3. Clean the intake air filter (navien-ncb-h-um-2501, p. 25). The manual’s procedure starts with the power off: press the Power button to turn the boiler off and disconnect its power supply, then unfasten the four latches (two at the top, two at the bottom) and remove the front cover. The filter is at the top left, held by one screw. Pull it out, remove it from its plastic assembly, dust it and rinse it under clean running water, and let it dry completely. Refit the filter and its screw, replace the front cover, reconnect the power and turn the boiler on (navien-ncb-h-um-2501, pp. 16–17). The manual says not to remove the front cover unless the power is turned off or disconnected (navien-ncb-h-um-2501, p. 5), and not to operate the boiler with the front cover open (navien-ncb-h-um-2501, p. 4).
4. Reset the boiler once: press Back on the front panel (navien-ncb-h-um-2501, p. 13).
5. If E110 comes back, the manual’s next step is an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 24).

The NCB-H manual asks for the air intake filter to be cleaned every 3–4 months (navien-ncb-h-um-2501, p. 16).

On the NFC-H, NFB-H and NHB-H, the E110 row says only “Check exhaust venting.” and does not say who checks (navien-nfc-h-um-c, p. 24; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). Their user’s manuals do give the owner the filter procedure above, with the same power-off steps at the start, and link a clogged filter to “Error Code 110”. They ask for the filter to be cleaned “as needed or as part of the annual maintenance” (navien-nfc-h-um-c, pp. 15–16; navien-nfb-h-um, pp. 15–16; navien-nhb-h-um, pp. 16–17). The reset on all three is the Back button (navien-nfc-h-um-c, p. 13; navien-nfb-h-um, p. 13; navien-nhb-h-um, p. 14).

When to call a licensed technician

• E110 returns after the exhaust check, a clean filter and one reset (navien-ncb-h-um-2501, p. 24).
• A vent or intake pipe is damaged, loose or separated (navien-ncb-h-um-2501, p. 4). The manual’s cover says installation and service must be performed by a qualified installer, service agency or the gas supplier (navien-ncb-h-um-2501, p. 1).
• Anything inside the boiler beyond the air filter. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-ncb-h-um-2501, p. 5).
• The seasonal inspection. A qualified technician should inspect the boiler at the beginning of every heating season and when there is a problem (navien-ncb-h-um-2501, p. 18).

Related codes: E109, E012, E762. All Navien boilers codes

Navien boiler error code E302: low water pressure

Checked October 2026

Short answer On Navien NFB-H, NHB-H, NCB700, NFB-C, NFB and NHB boilers, E302 means low water pressure; the NCB-H and NCB-E tables have E351 instead. The manuals give no refill step for owners: reset once, and if E302 stays, call a technician or Navien Technical Support. See what to check

What it means

E302 is “Low Water Pressure” in the NFB-H, NHB-H and NCB700 tables and “Low water pressure” in the NFB-C, NFB and NHB tables (navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24; navien-ncb700-io, p. 136; navien-nfb-c-um, p. 19; navien-nfb-um, p. 20; navien-nhb-um, p. 22).

The installation manuals say where it comes from. These boilers have a factory-installed, pressure-sensing low water cutoff (LWCO) with a minimum operation pressure of 6 psi by default. When the built-in water pressure sensor detects insufficient water level in the boiler, E302 appears on the front panel and the boiler needs a manual reset (navien-nfb-h-io, p. 19; navien-nhb-h-io, p. 17; navien-nfb-c-io, p. 22). The NCB700 manual says insufficient water pressure rather than level (navien-ncb700-io, p. 21).

Whether your boiler shows E302 depends on the series. The NCB-H, NCB-E, NFC-H and NFC tables have no E302. They have E351, the auto feeder (make-up water) valve code. The NFC-H and NFC installation manuals do mention E302 in their low water cutoff note, but E302 is not in their code tables or in the NFC-H user’s manual (navien-nfc-h-io, pp. 23, 127–128; navien-nfc-io, pp. 21, 101–102; navien-nfc-h-um-c, pp. 24–25).

Check these first

Navien’s user’s manuals give the owner no procedure for adding water or releasing pressure, and no normal pressure range. The NCB-H and NCB-E tables list “Add make-up water to the system if necessary.” for a different code, E777, without a procedure, and this page does not present it as an owner step (navien-ncb-h-um-2501, p. 26; navien-ncb-e-um, p. 22). What they do give for any error message is a reset, then a call:

1. Reset the boiler once. Press Back on the NFB-H, NHB-H and NFB (navien-nfb-h-um, p. 13; navien-nhb-h-um, p. 14; navien-nfb-um, p. 10), Reset on the NHB (navien-nhb-um, p. 11), or press and hold Reset on the NFB-C (navien-nfb-c-um, p. 10). The installation manuals say E302 needs a manual reset (navien-nfb-h-io, p. 19).
2. If E302 stays or comes back, the user’s manuals send you to an authorized technician, a licensed professional or Navien Technical Support at 1-800-519-8794 (navien-nfb-h-um, p. 22). Have the model number, serial number, date purchased, installation location and type, and the error code ready (navien-nfb-h-um, p. 27).
3. On the NHB-H, all repairs require pre-authorization by Technical Support: your installer or a licensed professional calls 1-800-519-8794, Option 2, from the installation site (navien-nhb-h-um, p. 29).

The panel shows the pressure. On the NFB-H and NHB-H a system pressure icon displays the internal water pressure of the boiler system, and Status Information lists “Water Press” in psi (navien-nfb-h-um, pp. 7, 13; navien-nhb-h-um, pp. 7, 13). The user’s manuals give no normal range for the owner. The owner’s daily task in the maintenance schedule is to check the pressure/temperature gauge for signs of higher than normal pressure, not low pressure (navien-nfb-h-um, p. 17).

When to call a licensed technician

• Any E302 that does not clear with one reset or comes back.
• The check in the table. The NFB-H, NHB-H and NCB700 tables say “Check water pressure.” without saying who checks or what reading is correct (navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24; navien-ncb700-io, p. 136).
• Checking the system’s water pressure. The figures in Navien’s manuals are for the installer and the service technician. The technician’s annual start-up list asks for a cold fill pressure of at least 6 psi on the NFB-H and NHB-H and at least 12 psi on the NFB-C, NFB and NHB (navien-nfb-h-um, p. 19; navien-nhb-h-um, p. 20; navien-nfb-c-um, p. 15; navien-nfb-um, p. 16; navien-nhb-um, p. 18). The NFB-H installation manual describes heating systems “operating with 12-80 psi water pressure at the boiler outlet” (navien-nfb-h-io, p. 19).
• Anything inside the boiler. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-nfb-h-um, p. 5).

Related codes: E351, E352, E353, E777. All Navien boilers codes

Navien combi boiler error code E351: auto feeder (make-up water) valve

Checked October 2026

Short answer On Navien NCB-H, NCB-E, NFC-H and NFC combi-boilers, E351 means an abnormal auto feeder (make-up water) valve; on the NCB-H it appears when the automatic refill is not completed after 5 minutes. Reset once; if it stays, contact Navien Technical Support. See what to check

What it means

E351 is the auto feeder valve code of four Navien combi-boiler series: “Abnormal Auto Feeder Valve” in the NCB-H table and “Abnormal Auto feeder valve (make-up water)” in the NCB-E and NFC tables (navien-ncb-h-um-2501, p. 25; navien-ncb-e-um, p. 22; navien-nfc-io, p. 101). The NFC-H uses one wording in each of its manuals (navien-nfc-h-um-c, p. 24; navien-nfc-h-io, p. 127).

The NCB-H installation manual says what sets it off. The boiler has a factory-installed, pressure-sensing low water cutoff with a minimum operation pressure of 7.3 psig. When the built-in water pressure sensor detects insufficient water level in the boiler system, the boiler refills itself automatically. If the refill is not completed after 5 minutes, E351 appears on the front panel and the boiler needs a manual reset (navien-ncb-h-io, p. 20).

The NFC-H and NFC installation manuals describe their low water cutoff differently: 6 psi by default, and E302 with a manual reset when the sensor detects insufficient water level (navien-nfc-h-io, p. 23; navien-nfc-io, p. 21). Yet E302 is not in either manual’s code table or in the NFC-H user’s manual, which list E351 (navien-nfc-h-io, pp. 127–128; navien-nfc-io, pp. 101–102; navien-nfc-h-um-c, pp. 24–25). Navien’s documents do not resolve this.

The NCB700 combi and the heating-only NFB-H, NHB-H, NFB-C, NFB and NHB have no E351; their low water code is E302. The NFB700-C table has neither code (navien-nfb700-c-io, pp. 119–120).

Check these first

For E351 the NCB-H and NCB-E tables give one action: contact Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 25; navien-ncb-e-um, p. 22). The user’s manuals give the owner no procedure for refilling the system. What they give for any error message is a reset, then a call:

1. Reset the boiler once. On the NCB-H press Back on the front panel (navien-ncb-h-um-2501, p. 13); on the NCB-E press Reset (navien-ncb-e-um, p. 11). The installation manual says E351 needs a manual reset (navien-ncb-h-io, p. 20).
2. If E351 stays or comes back, contact Navien Technical Support, as the table says (navien-ncb-h-um-2501, p. 25).
3. Have the model number, serial number, date purchased, installation location and type, and the error code ready (navien-ncb-h-um-2501, p. 64).

The NCB-H panel shows the system pressure, and Status Information has a “16. Water Pressure” item in psi (navien-ncb-h-um-2501, pp. 8, 12). The user’s manual gives no normal range for the owner. The owner’s daily task in its maintenance schedule is to check the pressure/temperature gauge for signs of higher than normal pressure (navien-ncb-h-um-2501, p. 18).

On the NFC-H, the user’s manual row reads “Check valve and supply water.” and does not say who checks (navien-nfc-h-um-c, p. 24). Its reset is the Back button (navien-nfc-h-um-c, p. 13).

When to call a licensed technician

• Any E351 that does not clear with one reset or comes back (navien-ncb-h-um-2501, p. 25).
• The valve and water supply check from the NFC-H table (navien-nfc-h-um-c, p. 24).
• Checking the system’s water pressure. The figures in Navien’s manuals are for the technician: the annual start-up list asks for a cold fill pressure of at least 12 psi on the NCB-H and NCB-E and at least 6 psi on the NFC-H (navien-ncb-h-um-2501, p. 20; navien-ncb-e-um, p. 18; navien-nfc-h-um-c, p. 19).
• Anything inside the boiler. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-ncb-h-um-2501, p. 5).

Related codes: E302, E352, E353, E777. All Navien boilers codes

Navien combi boiler error code E407: hot water outlet sensor

Checked October 2026

Short answer On Navien combi-boilers, E407 flags the domestic hot water outlet sensor (NCB-E and NFC: thermistor open or short circuit). Reset once; if E407 stays, contact Navien Technical Support, since the manuals give no owner step for the sensor. See what to check

What it means

E407 is a domestic hot water code, and only the combi-boiler tables have it. The NCB-H, NCB700 and NFC-H tables call it “Dom.Hot Water Outlet Sensor” (navien-ncb-h-um-2501, p. 25; navien-ncb700-io, p. 136; navien-nfc-h-um-c, p. 24). The older wording names the part and the fault: “Hot water outlet: thermistor open or short circuit” on the NFC and in the 2021 NFC-H installation manual, and “Hot water outlet thermistor open or short circuit” on the NCB-E (navien-nfc-io, p. 101; navien-nfc-h-io, p. 127; navien-ncb-e-um, p. 22). The heating-only tables (NFB-H, NHB-H, NFB, NHB, NFB-C, NFB700-C) have no E407.

Check these first

The NCB-H, NCB700, NCB-E and NFC tables give one action for E407: contact Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 25; navien-ncb700-io, p. 136; navien-ncb-e-um, p. 22; navien-nfc-io, p. 101). The user’s manuals give the owner no step for the sensor. What they give for any error message is a reset, then a call:

1. Reset the boiler once. On the NCB-H press Back on the front panel (navien-ncb-h-um-2501, p. 13); on the NCB-E press Reset (navien-ncb-e-um, p. 11).
2. If E407 stays or comes back, contact Navien Technical Support, as the table says (navien-ncb-h-um-2501, p. 25).
3. Have the model number, serial number, date purchased, installation location and type, and the error code ready (navien-ncb-h-um-2501, p. 64).

On the NFC-H, the user’s manual row reads “Check thermistor connector.” and does not say who checks (navien-nfc-h-um-c, p. 24). The manual gives the owner no procedure for it. It says not to remove the front cover unless the power to the boiler is turned off or disconnected, and not to repair or replace any part unless the manual specifically recommends it (navien-nfc-h-um-c, p. 5). The NFC-H reset is the Back button (navien-nfc-h-um-c, p. 13).

When to call a licensed technician

• Any E407 that does not clear with one reset or comes back (navien-ncb-h-um-2501, p. 25).
• The thermistor connector check from the NFC-H table (navien-nfc-h-um-c, p. 24).
• Anything inside the boiler. Navien tells owners not to repair or replace any part unless the user’s manual specifically recommends it (navien-ncb-h-um-2501, p. 5).

Related codes: E421, E441, E439. All Navien boilers codes

Navien boiler error code E762: vent pipe not fully inserted

Checked October 2026

Short answer On Navien NCB-H, NCB700, NFC-H, NFB-H and NHB-H boilers, E762 means the vent pipe is not fully inserted in the exhaust collar, and the boiler does not run. Reseating the pipe is installer work; call your installer or Navien Technical Support. See what to check

What it means

E762 is “Vent Pipe Not Fully Inserted” in the NCB-H, NCB700, NFC-H, NFB-H and NHB-H tables (navien-ncb-h-um-2501, p. 26; navien-ncb700-io, p. 137; navien-nfc-h-um-c, p. 25; navien-nfb-h-um, p. 23; navien-nhb-h-um, p. 24). The installation manuals tie it to the vent installation detector (VID). During installation, the VID detects whether the vent pipe is fully inserted into the collar, at least 2-3/4” (70 mm). A correctly sized vent pipe (2.0 inches) pushed fully in presses against a switch; if the pipe is not fully inserted, the unit displays an error message and does not operate (navien-ncb-h-io, p. 62; navien-ncb700-io, p. 62; navien-nhb-h-io, p. 55).

The VID text in these manuals is about installation. The user’s manuals separately ask for the vent termination and air intake supply to be inspected every year (navien-ncb-h-um-2501, p. 4).

The NCB-E, NFC, NFB, NHB, NFB-C and NFB700-C tables have no E762 (navien-ncb-e-um, p. 22; navien-nfc-io, pp. 101–102; navien-nfb-um, p. 20; navien-nhb-um, p. 22; navien-nfb-c-um, p. 19; navien-nfb700-c-io, pp. 119–120).

Check these first

The tables split here. On the NCB-H and NCB700 the action is “Contact technical support at 1-800-519-8794.” (navien-ncb-h-um-2501, p. 26; navien-ncb700-io, p. 137). On the NFC-H, NFB-H and NHB-H the user’s manual row says to insert the pipe into the exhaust collar to a stated depth (see the notes below). Inserting the vent pipe is venting work: the user’s manual cover says installation and service must be performed by a qualified installer, service agency or the gas supplier (navien-ncb-h-um-2501, p. 1). What an owner can do:

1. The owner maintenance schedule includes a monthly visual inspection of “the vent piping for signs of leakage and blockage” (navien-ncb-h-um-2501, p. 18). If any vent pipe, vent elbow or intake pipe is damaged, separated at a joint, or shows corrosion, rusting or melting, the manual says to turn the boiler off and discontinue use (navien-ncb-h-um-2501, p. 4).
2. Keep in mind Navien’s warning: do not operate the boiler without proper venting, because doing so may result in fire or carbon monoxide poisoning (navien-ncb-h-um-2501, p. 4).
3. Call the professional who installed the boiler or Navien Technical Support at 1-800-519-8794 (navien-ncb-h-um-2501, p. 64). On the NHB-H, all repairs require pre-authorization by Technical Support, and your installer or a licensed professional calls 1-800-519-8794, Option 2, from the installation site (navien-nhb-h-um, p. 29).

When to call a licensed technician

• Any E762. Seating the vent pipe at the right depth is part of the installation that the VID checks (navien-ncb-h-io, p. 62).
• Checking the pipe size. The VID text names a correctly sized vent pipe of 2.0 inches (navien-ncb-h-io, p. 62; navien-nfb-h-io, p. 57; navien-nfc-h-io, p. 65).
• Any damaged, loose or separated vent or intake pipe (navien-ncb-h-um-2501, p. 4).
• The seasonal inspection. A qualified technician should inspect the boiler at the beginning of every heating season and when there is a problem (navien-ncb-h-um-2501, p. 18).

Related codes: E110, E030. All Navien boilers codes