Navien E016: Overheat Protection Tripped

Navien error code E016 means the unit’s overheat protection tripped, shutting down the burner before the heat exchanger could reach an unsafe temperature. Scale buildup and restricted water flow are the most common underlying causes.

Illustration of a small temperature sensor positioned near a flue pipe inside a tankless water heater's access panel. — Illustration of a small temperature sensor positioned near a flue pipe inside a tankless water heater’s access panel.

Likely Causes, Ranked

Scale buildup in the heat exchanger
Reduces how efficiently heat transfers to the water, so metal temperatures climb.
Restricted water flow
A partially closed valve, a clogged inlet filter, or scale narrowing the flow path.
Failed temperature sensor
Less common, but a sensor reading incorrectly high can trip this protection without an actual overheat.

Step-by-Step Diagnosis

DIY SAFE
Check that both isolation valves are fully open

A partially closed valve restricts flow enough to trigger overheat protection.
DIY SAFE
Clean the inlet water filter if your model has one

Sediment buildup is a common, easy-to-miss restriction.
DIY WITH CAUTION
If the unit is overdue for a descaling flush, schedule one

Scale is the leading long-term cause of overheat-related faults on tankless units in hard-water areas.
PRO ONLY
If flow and scale both check out

Have a technician verify the temperature sensor and heat exchanger.

FAQ

How often should I flush my tankless unit to avoid this?

Most manufacturers recommend annually in hard-water areas, longer in soft-water areas — see our flush guide for the full schedule by water hardness.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

General overheat-protection pattern across tankless brands, consistent with scale/flow-restriction causes