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Quick answer from a licensed plumber: an E-code on the front panel of a Navien NPE-A2 or NPE-S2 names the fault, and Navien’s own user manual gives owners a first step for only a handful of them. E003 (ignition failure): make sure the main gas supply valve is open. E012, E109 and E110: clean the air intake filter. E016 and E030 (overheating): clean the cold water inlet filter and flush the heat exchanger. E004, E012 and E515: make sure the power cord is properly grounded. E760: routine service is due. E438 (circulation pump) and E788 (gas type mismatch) have their own checks, covered below. For every other code, the manual sends you to Navien Technical Support (1-800-519-8794) or a licensed professional. After you fix the cause, press the Back button to reset.
Safety first: if you smell gas, do not try to light any appliance, do not touch any electrical switch or use any phone in the building, and call your gas supplier from a neighbor’s phone (the fire department if you cannot reach them). That is Navien’s own instruction.
Codes With an Owner Step
These come from the “Understanding Error Codes” table in Navien’s User’s Information Manual for the NPE-180A2, 210A2 and 240A2 and the NPE-180S2, 210S2 and 240S2. The wording in the middle column is Navien’s. If your Navien is a different series, use the table in its own manual.
| Code | Navien’s reason | Navien’s action |
|---|---|---|
| E003 | Ignition failure | Make sure the main gas supply valve is open. |
| E004 | False flame detection | Make sure the electrical cord is properly grounded. |
| E012 | Flame loss | Clean the intake air filter; make sure the electrical cord is properly grounded. |
| E016 | Overheating of heat exchanger | Clean the cold water inlet filter; flush the heat exchanger. |
| E030 | Exhaust overheating (shuts down when flue temperature exceeds 149 °F / 65 °C) | Clean the cold water inlet filter; flush the heat exchanger. |
| E109 | Abnormal operation: fan motor | Clean the intake air filter. |
| E110 | Abnormal air pressure | Make sure the exhaust pipe is free of obstructions; clean the intake air filter. |
| E438 | Abnormal operation: circulation pump (with an air handler installed) | Check that the circulation pump is operating properly. |
| E515 | Abnormal operation: PCB | Make sure the electrical cord is properly grounded. |
| E760 | Flushing/service alarm | Contact the installer for routine service. |
| E788 | Abnormal operation: discrepancy with the gas type on the panel DIP switch setting and the panel | Match the gas type setting to the gas actually supplied (see below). |
Codes Navien Sends to Technical Support
For each of these, the manual’s only action is to contact Navien Technical Support at 1-800-519-8794. They involve sensors, valves, the circuit board, venting or the gas type — none of them are owner repairs.
| Code | Navien’s reason |
|---|---|
| E031 | Overheating of burner |
| E046 | Abnormal operation: limit control |
| E047 | Exhaust thermostat: thermistor open or short circuit |
| E060 | Abnormal operation: dual venturi |
| E407 | Hot water outlet: thermistor open or short circuit |
| E421 | Cold water inlet 1: thermistor open or short circuit |
| E432 | Cold water inlet 2: thermistor open or short circuit |
| E434 | Abnormal operation: water adjustment valve |
| E439 | Abnormal operation: flow sensor |
| E441 | Hot water inlet 2: thermistor open or short circuit |
| E445 | Abnormal operation: bypass mixing valve |
| E517 | Abnormal operation: DIP switch setting |
| E593 | Abnormal operation: front panel key |
| E594 | Abnormal operation: EEPROM |
| E615 | Abnormal operation: input and memory |
| E736 | Abnormal operation: cascade communication |
| E740 | Abnormal operation: outdoor temperature sensor (with an air handler installed) |
| E762 | Vent pipe not properly inserted |
| E773 | Using the wrong gas |
| E782 | Abnormal operation: main panel communication |
| E785 | Abnormal operation: flow switch/sensor (with an air handler installed) |
Our advice: E762 (vent pipe not properly inserted) and E773 (using the wrong gas) are about the exhaust and the fuel. Do not keep resetting either one; turn the heater off at the front panel and get it looked at.
Reset First, and Know What It Tells You
Navien says that if an error message appears you can try resetting the heater by pressing the Back button, that minor problems may clear that way, and that the heater keeps your settings during a power outage. If the reset does not hold, the code is real. Write it down before you call anyone, together with the model (NPE-A2 or NPE-S2) from the rating label.
E003: Ignition Failure
Navien lists a single owner action: make sure the main gas supply valve is open. Check the valve on the gas line at the heater. Our tip: if other gas appliances are also out, the problem is the supply, and that is a call to your gas utility. If the gas is on and E003 keeps coming back, what is left is on the gas supply side or inside the sealed cabinet, and that is a licensed professional’s or Navien’s job, not a homeowner repair.
I send an occasional note when a new guide goes up — repairs worth doing yourself, and the parts that actually last. No spam, no course funnel; written by a licensed Georgia plumber.
E012, E109 and E110: The Air Intake Filter
Navien says a clogged air intake filter will stop the heater and show Error Code 110, and that you should clean the filter every 3 to 4 months. For E110 it also says to make sure the exhaust pipe is free of obstructions — look at the outside termination for snow, leaves or nests you can clear safely. Navien’s steps for the filter:
- Press the Power button on the front panel to turn the heater off, then disconnect the power supply.
- Remove the front cover, then the screw that holds the air intake filter (top left of the heater), and pull the filter out.
- Remove the filter from its plastic assembly, clean it with a toothbrush and clean running water, and let it dry completely.
- Reassemble, secure it with the screw, replace the front cover, reconnect power and turn the heater on.
E016 and E030: Inlet Filter, Then Flush
Both codes are overheating: E016 at the heat exchanger, E030 when the flue temperature passes 149 °F (65 °C). Navien’s two remedies are the cold water inlet filter and a heat exchanger flush.
Cleaning the cold water inlet filter means draining the heater first. Navien’s drain steps:
- Put a bucket under the heater, press Power to turn it off, and close the gas valve. Navien warns the heater may stay hot for several minutes after it is turned off, so let it cool before you drain it.
- Close the water supply valve on the heater’s inlet (or the main, if there is no valve) and open all hot water faucets fully.
- On an “A2” model, remove the recirculation inlet filter and open the pump drain plug. Remove the cold water inlet filter and let the water drain.
- Rinse the filters under cold running water, scrubbing with a brush if needed, then reinsert and tighten them and close the drain plug.
- Refill by reversing the steps.
The flush is where Navien slows you down. It calls the procedure somewhat complicated, says to contact an authorized technician or licensed professional if you are unsure of any step, and warns that improper maintenance can void your warranty. Navien’s list is a bucket of 5 gallons or larger, a cleaning solution diluted with water, 3 hoses and a water circulation pump, and the heater needs isolation valves with service ports to connect them (our note); Navien circulates the solution for at least 45 minutes, rinses with fresh water for 5 minutes, then cleans out the cold water inlet filter again.
The Flush Kit, If You Flush It Yourself
Superior Pump 91660 Tankless Water Heater Descaler Pump Kit. The listing says it includes a 1/6 HP pump, a 3.5-gallon pail with a screw-top lid, two 3/4-inch garden-hose-thread (GHT) stainless steel hoses 6 feet long and a 7 oz packet of descaler powder, and that it is designed to clean and descale most tankless water heaters. Navien lists a bucket of 5 gallons or larger, so use one instead of the kit’s 3.5-gallon pail. Navien’s steps use 3 hoses, one of them on the pump inlet; the kit includes two, so add a third if your setup needs one. Use the cleaning solution your Navien manual or installer specifies. It was shipped and sold by Amazon.com, new and in stock, when we checked on September 24, 2026; details come from the Amazon listing, not from hands-on testing.
For the full walk-through, including the isolation valves you need before any of this works, see how to descale a tankless water heater, and for the other kits we looked at, the best water heater flush kits.
The Power Cord Codes: E004, E012, E515
For these, Navien says to make sure the electrical cord is properly grounded. The owner-level check is simple: the heater should be plugged straight into a working, grounded three-prong outlet. Testing the outlet’s ground or changing the wiring is a job for a licensed electrician, not a plumber or a homeowner. Both of those points are our advice, not Navien’s.
E788: Gas Type Mismatch
Navien’s instruction is to check the gas type supplied and match the gas type setting on the panel’s DIP switch and the panel. You can confirm whether the house runs on natural gas or propane; our advice is that changing the DIP switch setting is not an owner adjustment, and converting a heater from one gas to another is licensed gas work. If there is any doubt, leave the heater off and call Navien Technical Support.
No Code, But No Hot Water
Navien’s basic troubleshooting table covers the cases where nothing is displayed:
- No water at all from the hot tap: make sure the shutoff valves on the hot and cold pipes are open, the cold water inlet filter is clean and the heater is not frozen.
- Water runs cold, or turns cold and stays cold: clean the inlet filter and open the hot faucet all the way; Navien’s question is whether it draws at least 0.5 gallons per minute through the heater. With an external recirculation system, Navien asks whether there is a check valve on the return line.
- Not hot enough: Navien says to check the temperature setting and check for cross plumbing between the hot and cold lines.
Freezing: Keep It Plugged In
Navien says the freeze protection needs electricity and works whether the heater is switched on or off, as long as it stays plugged in, so do not unplug it except for routine maintenance. On A2 models, Navien also says not to close the gas valve except for routine maintenance, because that limits the extra freeze protection. If the power or gas must be off for an extended period, Navien says to drain the heater. Navien also says freeze damage is not covered by its limited warranty. If you are weighing a replacement, see Navien vs Rinnai.
If you suspect the heater has frozen, Navien’s steps are: turn it off at the front panel, close the gas valve, open the hot faucet nearest the heater, warm both heat exchangers with a hair dryer or portable electric heater, and check every few minutes until water runs. Then check the heater and piping for leaks; if you find any, or it does not work properly, contact an authorized technician or licensed professional.
When to Stop and Call a Licensed Professional
- You smell gas — follow the steps at the top of this page.
- Any code in the “Technical Support” table, especially E762 (venting) or E773 (wrong gas).
- E003 keeps returning with the gas supply valve open.
- A power-cord code keeps returning after you have confirmed a grounded outlet (Navien Technical Support or a licensed professional).
- You find a leak after a freeze, or you are not sure about any step of the flush.
FAQ
How do I reset a Navien tankless error code?
Press the Back button on the front panel. Navien’s manual says resetting may resolve minor problems and that the heater keeps your settings through a power outage. If the code returns, use the error-code table or call Navien Technical Support at 1-800-519-8794.
What does E003 mean on a Navien water heater?
E003 is ignition failure. The only owner action Navien lists is to make sure the main gas supply valve is open. If the gas is on and E003 keeps returning, the checks that remain are on the gas supply and inside the sealed cabinet, which is work for a licensed professional or Navien’s technical support.
How often should I clean the Navien air intake filter?
Navien says every 3 to 4 months. A clogged intake filter stops the heater and shows Error Code 110, and the manual also points to that filter for E012 (flame loss) and E109 (fan motor).
What does E760 mean on a Navien?
E760 is the flushing or service alarm. Navien’s instruction is to contact the installer to perform routine service, which normally means flushing the heat exchanger.
Can I flush my Navien tankless myself?
Navien prints the procedure in its user manual but calls it somewhat complicated, says to contact an authorized technician or licensed professional if you are unsure of any step, and warns that improper maintenance can void the warranty. Navien lists a bucket of 5 gallons or larger, a diluted cleaning solution, 3 hoses and a circulation pump; the heater also needs isolation valves with service ports (our note).
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Plumbing Picks is written by a Georgia journeyman plumber, and the license can be checked through the Georgia Secretary of State’s license verification portal. Every code meaning and step on this page comes from the manufacturer documents listed below, which we opened and read; where we add our own advice, the page says so. Product details come from the Amazon listing. Where a link goes to Amazon we may earn a commission at no extra cost to you. This page is general information for owners, not an offer of repair work. Nobody pays to be included here. More on who writes this and how we pick.
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Bottom Line
On a Navien NPE-A2 or NPE-S2, the codes you can act on are few and specific: open the gas valve for E003, clean the air intake filter for E012, E109 and E110, clean the inlet filter and flush for E016 and E030, confirm a grounded outlet for E004, E012 and E515, and schedule service for E760. E438 and E788 have their own checks above; everything else goes to Navien Technical Support or a licensed professional, and a code that survives a Back-button reset is telling you something real.