Navien tankless water heater error codes
32 codes that Navien publishes for its tankless water heaters, each with what it means, the likely cause, what you can safely check and when to call a licensed professional. Tap your code:
If you smell gas
Stop: do not reset, relight or check anything on this page. Navien’s own words, from the cover page of the NPE-2 User’s Information Manual, under “What to do if you smell gas”:
- Do not try to light any appliance.
- Do not touch any electrical switch; do not use any phone in your building.
- Immediately call your gas supplier from a neighbor’s phone. Follow the gas supplier’s instructions.
- If you cannot reach your gas supplier, call the fire department.
Calling from a neighbor’s phone means leaving the building first. Source: NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone. Everything else is for a licensed professional — in the manuals’ words, a qualified installer, service agency or the gas supplier. If you smell gas, do none of the checks: follow the maker’s gas-smell instructions at the top of the page. Codes that need one are marked Licensed pro.
Read this first
Navien condensing tankless water heaters show an E and three digits on the front panel (E003, E012, E110 …). This page follows the error-code chart in the User’s Information Manual of the NPE-2 series (NPE-180A2, NPE-210A2, NPE-240A2 and the S2 models), section 5.2. Navien’s chart gives an owner action for about a third of the codes — open the gas valve, clean a filter, flush the heat exchanger — and for the rest says to contact Technical Support. For minor problems Navien says resetting may help: press the Back button on the front panel. If a reset and the remedies below do not work, Navien says to contact an authorized technician, a licensed professional or its Technical Support at 1-800-519-8794.
E003 Ignition failure
- What it means
- The heater could not light its burner.
- Likely cause
- Navien’s one owner action is the main gas supply valve: gas not reaching the burner is the first suspect.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Make sure the main gas supply valve is open — Navien’s action for E003.
- Reset: press the Back button on the front panel, then open a hot tap.
- When to call a licensed professional
- If E003 comes back with the gas on, call Navien Technical Support, the installer or a licensed professional.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E012 Flame loss
- What it means
- The burner lit, then lost its flame.
- Likely cause
- A clogged air intake filter, or a power cord that is not properly grounded.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Clean the air intake filter as the manual’s section 4.5 describes (power off first; the filter sits at the top left behind the front cover). Navien says to clean it every 3–4 months anyway.
- Make sure the heater is plugged into a properly grounded outlet.
- When to call a licensed professional
- Call a licensed professional or Navien Technical Support if E012 comes back after the filter is clean.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E110 Abnormal air pressure (air intake or exhaust blocked)
- What it means
- The heater detects the wrong air pressure in its combustion air path and stops. Navien’s manual says a clogged air intake filter makes it stop with “Error Code 110”.
- Likely cause
- A blocked exhaust pipe, or an air intake filter clogged by dust or lint.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Make sure the exhaust pipe is free of obstructions — look at the vent end outside for anything blocking it.
- Clean the air intake filter as the manual’s section 4.5 describes.
- When to call a licensed professional
- If E110 stays with the vent clear and the filter clean, call a licensed professional or Navien Technical Support.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E016 Heat exchanger overheating
- What it means
- The heat exchanger got too hot.
- Likely cause
- Restricted water flow: a clogged cold-water inlet filter, or scale inside the heat exchanger.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Clean the cold-water inlet filter (manual section 4.4).
- Flush the heat exchanger (manual section 4.3).
- When to call a licensed professional
- Call a licensed professional or Navien Technical Support if E016 returns after cleaning and flushing, or if you cannot flush it yourself.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E030 Exhaust overheating
- What it means
- The heater shuts down because the flue (exhaust) temperature went above 149°F (65°C).
- Likely cause
- As for E016: a clogged cold-water inlet filter or a scaled heat exchanger.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Clean the cold-water inlet filter (manual section 4.4).
- Flush the heat exchanger (manual section 4.3).
- When to call a licensed professional
- Call a licensed professional or Navien Technical Support if E030 returns.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E109 Fan motor fault
- What it means
- The combustion fan is not running as it should.
- Likely cause
- Navien’s owner action points at a clogged air intake filter.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Clean the air intake filter (manual section 4.5).
- When to call a licensed professional
- Call a licensed professional or Navien Technical Support if E109 stays after the filter is clean.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E004 False flame detection
- What it means
- The heater senses a flame when there should be none.
- Likely cause
- Navien’s action points at the electrical ground.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Make sure the heater’s power cord is plugged into a properly grounded outlet.
- When to call a licensed professional
- If E004 stays, call a licensed professional or Navien Technical Support.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E515 Circuit board (PCB) fault
- What it means
- The main circuit board reports abnormal operation.
- Likely cause
- Navien’s one owner action is the ground of the power cord.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Make sure the heater’s power cord is plugged into a properly grounded outlet.
- When to call a licensed professional
- If E515 stays, call a licensed professional or Navien Technical Support.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E760 Flushing or service reminder
- What it means
- A reminder that routine service — flushing the heat exchanger — is due. Not a breakdown.
- Likely cause
- The service interval has run out.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Nothing to reset: the reminder is about the flush. The manual’s section 4.3 describes it.
- When to call a licensed professional
- Navien’s action is to contact the installer to perform routine service.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E438 Circulation pump fault (with air handler)
- What it means
- Only where a Navien air handler (space heating) is installed: the circulation pump is not working properly.
- Likely cause
- The circulation pump.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Check that the circulation pump is running — Navien’s action.
- When to call a licensed professional
- Call the installer or Navien Technical Support if the pump is not running.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E031 Burner overheating
- What it means
- The burner itself got too hot.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E046 Limit control tripped
- What it means
- Abnormal operation of the high-limit control, the safety switch that cuts the burner when something overheats.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E060 Dual venturi fault
- What it means
- Abnormal operation of the dual venturi, which sets the gas-and-air mix.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E047 E407 E421 E432 E441 Temperature sensor (thermistor) open or short circuit
- What it means
- A temperature sensor has an open or short circuit: E047 the exhaust sensor, E407 the hot water outlet sensor, E421 cold water inlet sensor 1, E432 cold water inlet sensor 2, E441 hot water inlet sensor 2.
- Likely cause
- A failed sensor or its wiring.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E434 E439 E445 Water valve or flow sensor fault
- What it means
- Abnormal operation of the water side: E434 the water adjustment valve, E439 the flow sensor, E445 the bypass mixing valve.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E517 E593 E594 E615 Control fault: settings, keys or memory
- What it means
- The controls report abnormal operation: E517 the DIP switch setting, E593 a front-panel key, E594 the EEPROM (memory), E615 input and memory.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E736 E782 Communication fault
- What it means
- The heater lost communication: E736 with the other heaters in a cascade (several heaters linked together), E782 with the main panel.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E740 E785 Air handler sensor fault
- What it means
- Only where a Navien air handler is installed: E740 the outdoor temperature sensor, E785 the flow switch or sensor.
- Likely cause
- Navien does not give the owner a cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support (1-800-519-8794), the installer or a licensed professional — Navien’s table gives no owner action for this code.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E762 Vent pipe not properly inserted
- What it means
- The vent pipe is not properly inserted into the heater.
- Likely cause
- The vent connection at the heater.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Contact Navien Technical Support, the installer or a licensed professional: the vent is part of the gas installation.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
E773 E788 Wrong gas, or gas type setting mismatch
- What it means
- E773: the heater is using the wrong gas. E788: the gas type set on the panel DIP switch and the gas type set on the front panel do not agree.
- Likely cause
- A heater set for natural gas on propane, or the reverse, or two settings that were not changed together.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Call the installer or a licensed professional. For E788 Navien’s action is to check the gas actually supplied and match both settings to it; for E773 it says to contact Technical Support. Running on the wrong gas is not something to test by trial.
Source: Navien, NPE-2 Condensing Water Heaters User’s Information Manual (NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2; version 1.0, 2020), section 5.2 Understanding Error Codes, pages 17–18 Checked 2026-09-29.
A code that is not listed here
The NPE-2 chart lists 32 codes, all on this page. Other Navien heaters, boilers and combi-boilers print their own charts in their own manuals; if your model is not an NPE-2, check its chart before using this one.
We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.
Related pages
Source
Every code on this page comes from this page, published by Navien and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.