Navien E016 Error Code — What It Means
The E016 code indicates your Navien tankless water heater has detected an abnormal heat-exchanger temperature condition and entered protection mode. The unit’s computer shut down the burner because heat is building up faster than water can carry it away.
This overheat fault is most often caused by restricted water flow or scale buildup inside the heat exchanger. The system needs sufficient flow through the exchanger to remove heat. When flow drops or mineral deposits insulate the metal, the temperature sensor triggers E016 and locks out the unit to prevent damage.
Common Causes
- Clogged inlet filter or strainer Debris or sediment in the cold-water inlet filter blocks flow into the heat exchanger, triggering overheat protection.
- Scale and calcification in the heat exchanger Mineral deposits coat the inside of the exchanger tubes, insulating them and preventing water from absorbing heat efficiently.
- Restricted water flow or closed valves Partially closed isolation valves, kinked supply lines, or undersized plumbing reduce flow through the unit.
- Faulty circulation pump or three-way valve A failed circulator or stuck valve prevents proper hot-water flow through the heat exchanger, especially on combi models.
- Defective flow sensor The flow sensor may falsely report low flow or fail to signal the board, causing the unit to run too hot.
Step-by-Step Fix
- Turn the unit off and wait at least 30 minutes for the heat exchanger to cool completely before you begin any work.
- Remove and clean the inlet water filter. Shut the cold-water isolation valve, unscrew the strainer housing at the inlet, rinse the screen under water, and reinstall it.
- Check all isolation valves and plumbing upstream and downstream of the unit to confirm they are fully open and that supply lines are not kinked or restricted.
- Inspect the heat exchanger for scale. If the filter was clean and flow is normal but the code returns, descale the unit using a flush kit and manufacturer-approved descaling solution according to your model’s service manual.
- Test the circulation pump and three-way valve (if your model is a combi boiler). Listen for the pump to run during a hot-water call and verify the valve moves freely.
- Check the flow sensor for debris or damage. Some models allow you to remove and inspect the turbine. Clean or replace the sensor if the blades are stuck or corroded.
- Reset the unit and test. Power the heater back on and open a hot-water tap to verify normal operation. If E016 reappears immediately, call a licensed technician for board-level or heat-exchanger diagnostics.
Parts Often Needed
| Part | Notes |
|---|---|
| Navien inlet water filter / strainer | Amazon | Match the thread size and filter micron rating to your model’s spec. |
| Navien flow sensor | Amazon | Model-specific. Verify the part number from your unit’s label or service manual. |
| Circulation pump (Navien) | Amazon | Required on combi models. Confirm voltage and connection type before ordering. |
| Descaling flush kit | Amazon | Includes hoses and pump. Use with Navien-approved descaler solution only. |
When to Call a Pro
Call a licensed plumber or Navien-certified technician if the E016 code returns after you have cleaned the inlet filter and confirmed water flow is normal. Persistent overheat faults usually mean scale inside the heat exchanger that requires a professional flush, a failed circulation pump or three-way valve, or a control-board issue. Do not attempt to disassemble the heat exchanger or test electrical components unless you have gas-appliance and electrical training. Overheat conditions can indicate unsafe combustion or venting problems that only a qualified technician should diagnose.