- Boilers
- Tankless gas water heater
E016
Navien E016 on a tankless water heater: heat exchanger overheating
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
The heater has detected overheating of the heat exchanger. Navien's owner remedies are to clean the cold water inlet filter and then flush the heat exchanger. Reset once with the Back button first.
Safety first
Stop and check this first
- If you smell gas: do not try to light any appliance, do not touch any electrical switch and do not use any phone in the building. Call your gas supplier from a neighbor's phone and follow its instructions; if you cannot reach it, call the fire department.
- Do not remove the front cover to look inside: Navien warns that operating the heater with the front cover open can cause fire or carbon monoxide poisoning, and that the cover may only come off with the power disconnected.
Safe checks you can perform
- One reset with the Back button
- Clean the cold water inlet filter
- Water hardness and last flush
- Heat exchanger flush
Leave these tasks to a qualified professional
- Do not attempt this professional task: Flush the heat exchanger
- Do not attempt this professional task: Assess water quality and treatment
- Do not attempt this professional task: Escalate if the code persists
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Flush the heat exchanger
What they doThe technician flushes the heat exchanger with a pump, hoses and a cleaning solution made for tankless water heaters or white vinegar, then rinses it and cleans the inlet filter.
They must show youthe heater running without E016 after the flush.
In writingthe date, the solution used and the result.
Assess water quality and treatment
What they doThe technician compares your water hardness with the water quality table in Navien's installation manual and advises on a softener or Navien's treatment option.
They must show youthe hardness value used.
In writingthe treatment and flushing frequency recommended.
Escalate if the code persists
What they doIf E016 continues after the filter cleaning and flush, the technician contacts Navien technical support for further diagnosis instead of replacing parts on the code alone.
They must show youwhat was checked.
In writingthe findings and any part replaced with its reason.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
One reset with the Back button
- Who:
- you.
- How:
- press the Back button on the front panel. Navien's manual says resetting may solve the problem when an error appears.
- Result that matters:
- whether E016 comes back.
- If the heater runs normally:
- note the date; if E016 returns later, mention that it was reset before.
- If E016 returns:
- do not keep resetting; move on to the inlet filter.
- Evidence to keep:
- photo of the code before and after the reset.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
Clean the cold water inlet filter
- Who:
- you, following the user's manual, or your installer if you are unsure.
- How:
- drain the heater as Navien describes: press the Power button to turn it off, close the gas valve and the water supply valve on the inlet, open the hot water faucets, place a bucket underneath and remove the cold water inlet filter. Rinse it under cold running water, scrub it with a brush if needed, refit and tighten it, then refill by reversing the steps.
- Result that matters:
- a clean filter firmly refitted.
- If E016 clears:
- note the date and keep cleaning it as part of maintenance.
- If E016 returns:
- the heat exchanger flush is the next step.
- Evidence to keep:
- photo of the filter before and after cleaning.
Navien warns the heater can stay hot for several minutes after it is turned off; wait until it has cooled. Do not remove the front cover.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
Water hardness and last flush
- Who:
- you.
- How:
- check whether a water softener or treatment device is installed and when the heat exchanger was last flushed. Navien's installation manual sets flushing frequency by water hardness when no treatment device is installed.
- Result that matters:
- whether scale is a plausible cause.
- If the water is hard and there is no treatment or recent flush:
- ask for the flush.
- If it was flushed recently:
- tell the technician; other causes become more likely.
- Evidence to keep:
- maintenance invoices or water report.
Evidence: Navien NPE-A2 and NPE-S2 installation and operation manual
Heat exchanger flush
- Who:
- an authorized technician or licensed professional.
- How:
- with the heater off and the power disconnected, closes the hot and cold valves, connects a circulation pump and hoses to the valve kit, circulates a cleaning solution for at least 45 minutes, rinses with water for 5 minutes and cleans the cold water inlet filter, as Navien's manual describes.
- Result that matters:
- whether E016 stops after the flush.
- If it stops:
- keep the flush date and follow the water treatment advice.
- If E016 remains:
- the owner remedies are exhausted; Navien says to contact an authorized technician, a licensed professional or its technical support.
- Evidence to keep:
- service report with the flush date and the code after it.
Navien calls the flush a somewhat complicated procedure and says to contact an authorized technician or licensed professional if you are unsure; improper maintenance can void the warranty.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual · Navien NPE-A2 and NPE-S2 installation and operation manual
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Navien
- Product type
- Tankless gas water heater
Known code variants
- calentador Navien E016
- E016
- Navien 016
- Navien E016
- Navien E016 overheating
- Navien E016 sobrecalentamiento
- Navien error E016
What it means
Navien defines E016 as overheating of the heat exchanger. Its user manual gives two remedies: clean the cold water inlet filter and flush the heat exchanger, which points to restricted water flow and scale. The installation manual links scale to water hardness and sets flushing by hardness when no treatment device is fitted. If the code persists after both steps, Navien refers you to a technician. The code alone does not prove a part has failed.
Warnings and stop conditions
- Criticalsource verified
If you smell gas: do not try to light any appliance, do not touch any electrical switch and do not use any phone in the building. Call your gas supplier from a neighbor's phone and follow its instructions; if you cannot reach it, call the fire department.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
- Highsource verified
Do not remove the front cover to look inside: Navien warns that operating the heater with the front cover open can cause fire or carbon monoxide poisoning, and that the cover may only come off with the power disconnected.
Evidence: Navien NPE-A2 and NPE-S2 installation and operation manual
Symptoms and causes
Probable causes · in order
- Clogged cold water inlet filterPossible
The first remedy Navien gives for E016. More likely if the filter has not been cleaned recently or hot water flow has dropped.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
- Scale in the heat exchangerPossible
Navien's second remedy for E016 is flushing the heat exchanger. More likely with hard water and no treatment device or recent flush.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual · Navien NPE-A2 and NPE-S2 installation and operation manual
Virtual technician
Does E016 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Navien NPE-A2 and NPE-S2 user's information manual
Navien · 2020 · manual
- 2
Navien NPE-A2 and NPE-S2 installation and operation manual
Navien · 2026 · manual
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