All tankless water heaters will surprise you with an unexpected error code eventually. Unfortunately, it’s always at an inopportune time. The same holds true for Navien tankless water heaters.

Although not a pleasant experience, this error code, on the other hand, can help you determine what is wrong with your tankless water heater so that you can take appropriate action.

When an error code occurs, you’ll likely hear an audible “beeping” alarm. If you have no hot water, you may have overwhelmed your tankless water heater’s capacity or have at least one error code.

This guide will discuss and go over the Navien tankless water heater error codes, their meaning, troubleshooting, and more. So let’s take a look.

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Error Code E001: Heat Exchanger Overheating

Navien error code E001 is caused by an overheating heat exchanger. To fix Navien error code E001, you may need to clean the strainer and flush the heat exchanger. Ensure the flow rate and the PCB voltage at the pump are within spec and that the water circulates properly.

We have a how-to guide for tankless water heater maintenance. In Easy Maintenance Tips for Tankless Water Heaters w/Photos will outline how to perform tankless water heater flushing and other maintenance.

Error Code E002: Low Pressure on the Heating Side

Navien error code E002 means there is low pressure on the heating side. Navien error code E002 can be caused by low water pressure, so you have to ensure that the unit receives enough water. You may also need to restart the unit to fix this error code.

Error Code E003: Ignition Failure

Navien error code E003 indicates a failure in the ignition of the unit. If your Navien is displaying an error code E003, ensure the gas supply is on and working, that the unit is powered, the ground wire is connected, and that the igniter is producing a spark.

Clean or replace the igniter electrode or the PCB if necessary.

This is also occurs from a power failure. If you live in an area that experiences routine blackouts or power failures, you may need to look into a battery backup power supply for your tankless water heater.

Error Code E004: False Flame Detection

Navien error code E004 is an indication that the unit is detecting a false flame. To troubleshoot Navien error code E004, confirm that the ground wire is connected correctly and is not loose. In addition to that, check whether the igniter is producing a spark.

Error Code E011: High Pressure on Heating Side

Navien error code E011 means there is high pressure on the heating side. This error code may be fixed by switching off the unit, draining the water to release the pressure, and switching it back on. If the error persists, check the condition of the sensor. If necessary, replace the sensor.

Error Code E012: Flame Loss

Navien error code E012 means there is a flame loss. To troubleshoot and fix Navien error code E012, confirm that the main gas valve is open and the gas pressure is within spec. Also, check the intake air filter, the ground wire, power supply, and the wiring at the heat exchanger.

You may also need to check and adjust the anti-short cycle timing as it can also cause an error code E012 in some instances.

Error Code E016: Heat Exchanger Overheating

Navien error code E016 means the heat exchanger is overheating. To fix and troubleshoot Navien error code E016, switch the unit off for 30 seconds and then back on. Check and clean the cold water filter and strainer, and flush the heat exchanger. Check the high limit switch, the 3-way valve, and the PCB.

Error Code E030: Abnormal Exhaust Temperature

Navien error code E030 is caused by an overheating exhaust. To troubleshoot and fix Navien error code E030, switch the unit off for 30 seconds and then power it back on. Check the strainer and the heat exchanger. Clean the strainer and flush the heat exchanger if needed.

The unit will cease working if the exhaust temperature exceeds 230°F (110 °C) for more than 10 seconds.

Error Code E046: Heat Exchanger Error

Navien error code E046 means that there is a short at the heat exchanger thermistor. To fix Navien error code E046, check the condition of the wiring at the heat exchanger thermistor. Ensure there are no loose connections and the wiring is not damaged.

Navien error code E046 can also indicate a limit control, in which case it is advisable to contact a licensed contractor for further help.

Error Code E047: Exhaust Thermistor Error

Navien error code E047 is an indication of a problem in the operation of the exhaust thermistor. Navien error code E047 can be caused by an open or shorted exhaust thermistor, in which case to fix this error code, you need to check the connection and wiring at the exhaust thermistor.

Error Code E060: Dual Venturi Limit Switch Error

Navien error code E060 means a problem with the dual venturi limit switch. If your Navien displays an error code E060, you need to check the dual venturi connection. In some instances, the dual venturi may need to be fully replaced to fix this error code.

Error Code E109: Fan Motor Activity Error

Navien error code E109 indicates an error with the fan motor. To troubleshoot Navien error code E109, check and clean, if necessary, the air intake filter and the fan motor. If the error code persists, measure the PCB’s voltage and replace the fan if the voltage is within spec.

Error Code E110: Exhaust Blockage

Navien error code E110 means there is an exhaust blockage. To fix the Navien error code, E110 ensures nothing obstructs or blocks the exhaust pipe and that the exhaust pipe is clear. In addition to that, assess the condition of the intake air filter and clean it if necessary.

This error code can be caused by condensate blockage as well. If the error code persists after resetting the unit, you may need to replace the air pressure sensor.

Error Code E127: APS Error (Open, Short, Initial Value or No Response)

Navien error code E127 is indicative of a problem with the air pressure sensor (APS). Error code E127 can be caused by an open or shorted APS. Switch it off the unit and inspect the condition of the APS. If the error code persists after a reset, you may need to replace the APS.

Error Code E205: H/E Outlet Error: Thermistor Open or Short

Navien error code E205 indicates a problem with the operation of the heating supply thermistor. An open or shorted thermistor can cause the Navien error code E205. To fix this error code, inspect the heating supply thermistor’s condition and the pump wiring connectors.

Error Code E218: H/E Inlet Error: Thermistor Open or Short

Navien error code E218 means there is a problem with the operation of the heating return thermistor. An open or short thermistor can cause the Navien error code E218. To fix this error code, inspect the heating return thermistor’s condition and the pump wiring connectors.

Error Code E302: Low Water Pressure Error

Navien error code E302 means that the water pressure is too low. If your Navien is displaying an error code E302, check the water feeder valve and the water pressure and the water pressure relief valve. Replace any parts if needed.

Error Code E352: High Water Pressure Error

Navien error code E352 is indicative of high water pressure. If your Navien displays an error code E352, you need to check the water pressure is within good rangers and check the activity of the feeder valve and the water pressure relief valve.

Error Code E353: Water Pressure Sensor Error

Navien error code E353 indicates a problem with the water pressure sensor. An open or shorted sensor can cause Navien error code E353. Check and ensure the water pressure sensor and wiring are in good working condition, and there are no loose connections. If needed, replace the sensor.

Error Code E407: Hot Water Outlet 1: Thermistor Open or Short

Navien error code E407 is a sign of a problem with the hot water outlet thermistor. An open or shorted sensor causes the Navien error code E407. To fix it, check the thermistor’s condition and wiring. If necessary, replace the thermistor.

Error Code E421: Cold Water Inlet 1: Thermistor Open or Short

Navien error code E421 means there is a problem with the cold water inlet 1 thermistor. An open or shorted sensor causes the Navien error code E421. To fix it, check the thermistor’s condition and wiring. If necessary, replace the cold water inlet thermistor.

Error Code E432: Cold Water Inlet 2: Thermistor Open or Short

Navien error code E432 is a sign of a problem with the cold water inlet 2 thermistor. An open or shorted sensor causes the Navien error code E432. To fix it, check the thermistor’s condition and wiring. If necessary, replace the thermistor.

Error Code E434: Abnormality in Water Adjustment Valve

Navien error code E434 means there is a problem with the water adjustment valve. The Navien error code E434 can be caused by an open or shorter water adjustment valve. Switch the tankless water heater off and inspect the condition and wiring of the valve. If necessary, call for a service.

Error Code E438: Abnormality in Circulation Pump

Navien error code E438 means there is a problem with the circulation pump. To troubleshoot this error code, check the water supply and circulators, the flow sensor, and the pump. In the case of an error code E438, you may need to replace the pump, flow sensor, or PCB.

Error Code E439: Abnormal Flow Sensor

Navien error code E439 is indicative of a problem with the flow sensor. Error code E439 can be caused by a faulty flow sensor, PCB, or no cold water supply.

To fix this error code, check if there is water flow while the cascade system is switched off. If there is water flow, clean and inspect the condition of the flow sensor connector.

Error Code E441: Hot Water Outlet 2: Thermistor Open or Short

Navien error code E441 is a sign of a problem with the hot water outlet 2 thermistor. An open or shorted sensor causes the Navien error code E441. To fix it, check the thermistor’s condition and wiring. If necessary, replace the thermistor.

Error Code E445: Abnormal Mixing Valve

Navien error code E445 indicates an abnormality in the mixing valve. The Navien error code E445 is typically caused by a faulty feedback sensor, damaged, opened, shorted, or blocked mixing valve, or a defective PCB. If needed, call a licensed technician.

Error Code E480: External Tank Thermistor Open or Short (System Boiler Thermistor Setting Only)

Navien error code E480 means there is a problem with the external tank thermistor, typically caused by an open (at temperatures below 14°F) or shorted sensor. Check the sensor’s connectors to ensure they are installed correctly and are not wet. If required, replace the tank thermistor.

Error Code E515: PCB Error

Navien error code E515 indicates an issue with the PCB. In the case of an error code E515, the PCB, PCB’s monitoring device, igniter, fan, dual venturi, and the 3-way valve should all be inspected. Ensure they are in good condition and properly connected to the PCB.

Error Code E517: DIP Switch Setting Error

Navien error code E517 signifies a problem with the dip switch. To troubleshoot and fix Navien error code E517, you need to check the dip switches on the unit’s front panel and the PCB. If the error persists and everything looks good, call a licensed technician.

Error Code E593: Abnormal Panel Key

Navien error code E593 is caused by a problem with the operation of the front panel keys. To fix the Navien error code E593, you need to inspect if the panel keys operate as they should. If they do restart the unit and if they don’t replace the front panel.

Error Code E594: Partial PCB Communication Error

Navien error code E594 indicates a partial PCB communication error or an EEPROM error. Check the unit’s PCB for any damage or wiring issues. If the error persists and nothing looks out of the ordinary, contact a licensed contractor to evaluate the condition of your Navien tankless water heater.

In addition to that, you may also need to check the condition and wiring of the exhaust sensor, flame rod, and pressure sensor to ensure they are all in good condition.

Error Code E615: Input and Memory Error

Navien error code E615 can indicate an input data error or a memory error. Reset the unit and check the PCB and the condition and the wiring of the exhaust sensor, flame rod, and pressure sensor. Measure the pressure sensor’s output voltage and ensure it is within range. Call for service if needed.

Error Code E736: Abnormal Cascade Communication

Navien error code E736 indicates a problem with the cascade communication. Ensure that the PCB version is compatible and check the ready-link cascade cable is installed correctly and the cascade settings. If the error does not go away after resetting the unit, contact a licensed technician.

Error Code E740: Outdoor Sensor Error

Navien error code E740 means there is a problem with the outdoor temperature sensor. An open or shorted sensor can cause Navien error code E740. To fix it, ensure that the sensor’s wiring is in good condition and working correctly and that the outdoor reset curve is dialed in properly.

See our article Can Water Heaters Be Installed Outside: What You Should Know for more information on outdoor tankless water heater models.

Error Code: E760: Flushing Alarm

Navien error code E760 is a flushing service alarm. This error code is not an error code per se but rather a reminder. If your Navien tankless water heater displays an error E760, this means that you need to flush the heat exchanger.

Error Code E782: Main Panel Communication Error

Navien error code E782 indicates a communication error within the main panel. To troubleshoot the Navien error code E782, inspect the condition and operation of the PCB. To fix this error, you may need to have a licensed contractor assess your unit’s condition and replace the PCB if necessary.

Error Code E783: OT-remote Controller Error

Navien error code E783 means there is a problem with the operation of the OT-remote controller. Inspect the condition of the controller and, if necessary, replace it.

Error Code E785: Abnormal Flow Switch Operation

Navien error code E785 means there is a problem with the operation of the external flow switch. Check the cold water line and the condition of the flow switch. Check if the flow switch is in the off or on position and the thermal block’s resistance. If needed, replace the controller or the sensor.

Error Code E787: Device Reset Error

Navien error code E787 indicates that there has been a problem while the unit has been reset. Please switch off the unit for at least 30 seconds and ensure that everything works correctly, then power it back on. If the error code persists, have a technician evaluate the unit’s condition.

Tankless water heaters last 20 years on average and during that time you’re sure to have at least one of these Navien error codes. When buying a tankless water heater, we hope you find this guide helpful and will bookmark it for further reference.