How to Reset a Navien Tankless Water Heater

The Short Answer: On current Navien NPE-A2 and NPE-S2 heaters, you reset by pressing the Back button on the front panel. Older NPE-A/S and indoor NPN models have a dedicated Reset button, and outdoor NPN units reset from the remote (press OK once; “RST” appears). Navien’s manuals say not to unplug the heater except for routine maintenance, so use the button. If the code comes straight back, the cause is still there.

Which button resets your model

The model number is on the rating label on the side of the cabinet. Navien’s owner manuals give a different reset button for each line:

Before you reset, write down the code. The NPE-2 user’s manual (opens in a new tab) describes a reset as a first step for minor problems. If the code returns, the troubleshooting table and an authorized technician are the next steps. On NPE-A2/S2 models the front panel also keeps a list of the 10 most recent errors (Menu, then Error History), which is useful to show the technician.

Don’t unplug it to reset

It’s tempting to pull the plug, but Navien’s manuals say, in their freeze-protection section: “Do not unplug the power supply cord, except for routine maintenance.” The heater has a freeze protection function that needs electricity. It keeps working whether the heater is switched on or off, as long as the cord stays plugged in. Navien warns that freezing damage may occur if the heater loses power, which matters most in a cold garage or on an outside wall. Use the button for your model instead.

Your settings aren’t lost in a power outage: the NPE-2 and NPN manuals both say the heater keeps them. After an outage, see Navien tankless during and after a power outage.

Errors that clear themselves

The NPE-A2/S2 installation manual (opens in a new tab) describes “level 1” errors. The display flashes red and shows the error icon, but the heater keeps running. These clear automatically once the problem is resolved; pressing Back clears them too, but only if the problem has been resolved.

The NR-21DU remote’s manual (opens in a new tab) adds that, depending on the severity of the error, the heater either stops or runs with limited function. Either way, a reset only helps after the cause has been fixed.

When a reset won’t fix it

A reset clears the message, not the cause. Navien’s owner tables give these owner-level checks for the most common codes on NPE-2 models:

• E003 (ignition failure): make sure the main gas supply valve is open. More in Navien E003.
• E012 (flame loss): clean the intake air filter and make sure the cord is plugged into a properly grounded outlet.
• E016 and E030 (overheating): clean the cold water inlet filter. The manual also lists flushing the heat exchanger. See Navien goes cold after a few minutes.
• E110 (abnormal air pressure): make sure the exhaust pipe is free of obstructions and clean the intake filter.

Codes such as E773 (wrong gas type) or the thermistor and valve codes in the E400s list “Contact Technical Support” as the only action. Resetting them repeatedly won’t help. The full list is in Navien tankless error codes.

Things not to do

• Don’t use the Factory Reset in the installer menu. The NPE-2 installation manual describes it as initializing all parameter settings to factory defaults, which can undo settings the installer made for your system.
• Don’t change DIP switches to clear a gas-type code.
• Don’t keep resetting an ignition code. Each attempt sends gas through the burner. If the same code returns after one reset and the owner check, call for service.

Navien technical support is 1-800-519-8794, the number printed in the NPE-2 manual. Have the model, serial number and the code ready.

Frequently Asked Questions

Q: Where is the reset button on my Navien NPE-240A2? A: There isn’t a separate one. On the NPE-A2 and NPE-S2, the Back button (the arrow on the front panel) does the reset.

Q: The display flashed red but I still have hot water. Do I need to reset? A: On NPE-A2/S2 models that’s usually a level 1 error, which doesn’t stop the heater and clears on its own once the cause is resolved. Note the code from the error history and check it in the code table.

Q: Will resetting clear the scale or flushing reminder? A: The remote clears its scale alarm by holding OK for two seconds until “RST” shows, but the reminder exists because the heat exchanger needs descaling. Clear it after the flush is done, not instead of it.