DIY Error Codes

Navien NPE-2 tankless water heater error E016

Overheating of heat exchanger

Navien's listed fixes: clean the cold water inlet filter, then flush the heat exchanger.

Gas appliance. Power off and let it cool before any maintenance.
Why
If you smell gas: do not try to light any appliance, do not touch any electrical switch, and do not use any phone in your building. Leave and call your gas supplier from a neighbor's phone; if you cannot reach them, call the fire department. Navien: turn the water heater off and disconnect the power supply before maintenance. It can stay hot for several minutes after it is turned off; wait until it cools to avoid burns. Water at or above 125 °F (52 °C) can cause instant scalding, severe burns, or death.

Fix it step by step

Step 1 of 3

  1. Clean the cold water inlet filter

    • 30 min
    • Bucket, Soft brush
    • DIY

    Safety: Gas appliance. Power off and let it cool before any maintenance.

    Drain the heater, then rinse and brush the inlet filter.

    Why & details

    Clean the cold water inlet filter.

    Navien sections 4.2 and 4.4: press Power off, close the gas valve, close the cold water supply valve, open hot faucets to drain the lines, put a bucket under the heater and remove the inlet filter (and the recirculation inlet filter and pump drain plug on A2 models). Rinse the filter under cold running water, brush if needed, reinstall and tighten, then refill by reversing the steps.

    Did the code clear?

  2. Flush the heat exchanger (or have it flushed)

    • 1.5 hr
    • Flushing kit (pump, 3 hoses, 5-gal bucket), Service valves
    • Caution

    Safety: Gas appliance. Power off and let it cool before any maintenance.

    Navien calls this a somewhat complicated procedure. If unsure, use a licensed pro.

    Why & details

    Flush the heat exchanger (or have it flushed).

    Navien section 4.3: with the heater off and power disconnected, close the hot and cold service valves, connect a circulation pump and hoses to the service valves, and circulate cleaning solution diluted with water through the heater from a 5-gallon bucket for at least 45 minutes, then rinse with fresh water for 5 minutes, clean the inlet filter, and restore power. Navien warns that improper maintenance can void the warranty and says to contact an authorized technician or licensed professional if you are unsure about any step.

    Did the code clear?

  3. Call a licensed pro

    • Decision
    • None
    • Pro decision

    Stop here and book a qualified technician.

    Why & details

    Call a licensed pro.

    If E016 returns after cleaning and flushing, contact Navien Technical Support or a licensed pro.

    Still showing E016?Still E016 → see the partNeed a pro → call a pro

Code cleared. Nice work.

Watch the display for a day to make sure it stays clear.

Back to top

Fixed after any step? Watch the display for a day to make sure it stays clear. Still E016 after step 3? See the replacement part or call a pro.

What E016 means

The heat exchanger got too hot. Navien says clean the cold water inlet filter and flush the heat exchanger.

More detail
Navien's error-code chart (section 5.2) lists E016 as "overheating of heat exchanger". If the listed remedies do not resolve the problem, Navien says to contact Technical Support.

5-minute checks

Full answer & models

Navien E016 on the NPE-2 means: overheating of heat exchanger. Navien's listed fixes: clean the cold water inlet filter, then flush the heat exchanger.

Applies to: NPE-180A2NPE-210A2NPE-240A2NPE-180S2NPE-210S2NPE-240S2
Also searched as: Navien error E016, Navien E016, Navien error code 016, Navien 016 code

Call a pro if…

  • You are not comfortable with the flushing procedure (Navien recommends a pro if unsure).
  • E016 returns after cleaning and flushing.

Part you'll likely need

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Only if you are comfortable with the manual's flushing procedure.

Tankless water heater flushing kit (circulation pump, hoses and bucket)

Navien NPE-2 User's Information Manual, §4.3 Flushing the Heat Exchanger, p.12, lists the items to gather: "A bucket that is 5 gallons or larger", "Cleaning solution diluted with water", "3 hoses" and "A water circulation pump". Navien cautions (p.12): "Flushing the Heat Exchanger is a somewhat complicated procedure." "If you are uncertain about any of the steps in the procedure, contact an authorized technician or licensed professional."

Fits: Heaters with hot and cold service (isolation) valves

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FAQ

What does Navien E016 mean?

Overheating of the heat exchanger, per the NPE-2 error-code chart.

Will flushing void my warranty?

Navien warns that improper maintenance can void the warranty. If unsure, have a licensed pro flush it.

Source: Navien NPE-2 User's Information Manual (NPE-A2/NPE-S2), Section 5.2 Understanding Error Codes, Sections 4.2-4.5 Maintenance. Written by the DIY Error Codes team. Updated 2026-10-16. DIY Error Codes is independent and not affiliated with or endorsed by Navien.