Navien E016 Error Code

What does Navien E016 mean?

E016 means the heat exchanger has reached an unsafe temperature and the high-limit switch has cut the burner to prevent damage. This is most commonly triggered by scale buildup inside the heat exchanger reducing water-side heat transfer, or by restricted water flow through a clogged inlet filter or partially closed valve. The unit will not fire again until the root cause is resolved.

Symptoms

• Unit shuts down mid-cycle with E016 displayed on the panel.
• Hot water output is reduced or absent before the error appears.
• Unit trips repeatedly after resetting without producing full hot water.
• Audible banging or kettling from the heat exchanger before shutdown.

Common causes

• Mineral scale and calcification inside the heat exchanger from hard water.
• Cold water inlet filter clogged with sediment, restricting flow.
• Water adjustment valve partially closed or malfunctioning.
• Recirculation pump failure causing stagnant water in the heat exchanger.
• High-limit thermistor wiring loose or damaged, causing premature shutdown.
• Excessively high inlet water temperature in recirculation systems.

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Diagnostic steps

1. Shut down and let the unit cool

   Turn the unit off at the power button and wait at least 30 minutes before restarting. Attempting to reset immediately while the heat exchanger is still hot will produce another immediate lockout.

2. Clean the cold water inlet filter

   Close the cold water supply valve, remove the inlet filter screen from the cold-side service port, rinse under running water, and reinstall. Inspect the mesh for tears that would allow debris to pass through.

3. Check the water adjustment valve

   Locate the automatic flow adjustment valve in the service manual and verify it is fully open and operating freely. A stuck or partially closed valve starves the heat exchanger of cooling flow.

4. Descale the heat exchanger

   Connect a descaling pump and run a food-grade descaling solution (diluted white vinegar or a commercial heat exchanger cleaner) through the unit per Navien's flushing procedure. Scale accumulation is the primary long-term cause of E016 in hard-water areas.

5. Inspect high-limit thermistor wiring

   After the unit is cool, check the wiring harness connector at the high-limit thermistor for corrosion or looseness. Reseat the connector and test for continuity with a multimeter.

When to call a professional

If E016 returns after descaling and clearing the inlet filter, a technician should inspect the heat exchanger for pinhole leaks caused by prolonged overheating and assess the recirculation pump and 3-way valve. Heat exchanger replacement requires draining the system, working on refrigerant-side connections in some models, and pressure-testing — this is not a DIY repair.