Navien Water Heater Error Code 006: How to Fix It

Q: What causes Navien error code 006?

Error code 006 is triggered by the unit's overheat protection circuit when internal temperatures exceed safe limits. The most common causes are low water flow (clogged inlet filter or partially closed valve), scale buildup in the heat exchanger, a failed high-limit cutoff sensor, a faulty thermistor giving incorrect temperature readings, or blocked exhaust venting on gas models.

Q: Can I just reset error code 006 and keep using my Navien?

A reset may temporarily clear the error, but if you have not identified and fixed the underlying cause, the error will return — often very quickly. Repeatedly running the unit while it is overheating can permanently damage the heat exchanger and other components. Always investigate the root cause before relying on repeated resets.

Q: How do I prevent Navien error code 006 from coming back?

Annual maintenance is the best prevention. Descale the heat exchanger every 1–2 years (more often in hard water areas), clean the cold water inlet filter screen every 6–12 months, ensure all water supply valves are fully open, and check that exhaust venting is clear and unobstructed before winter. Installing a whole-house water softener or descaler also significantly reduces scale buildup.

Q: How much does it cost to fix Navien error code 006?

If it is just a clogged filter or the unit needs descaling, the cost is minimal — under $20 for descaling supplies and about an hour of your time. Replacing a thermistor or high-limit sensor typically costs $20–$60 in parts if you do it yourself, or $150–$350 with a professional service call. If the heat exchanger is damaged, replacement can run $500–$1,000 or more including labor.

Q: Is Navien error code 006 dangerous?

Yes, this is a high-severity error and should be taken seriously. The overheat protection exists to prevent damage to the unit and potential safety hazards including extremely hot water, component failure, or — on gas models — improper combustion conditions. Do not continue using the unit without resolving the issue. If you smell gas or suspect a venting problem, shut off the gas supply and call a professional immediately.

Abstract

Navien error code 006 is an overheat protection fault, meaning your tankless water heater has detected temperatures that are dangerously high and has shut itself down to prevent damage or injury. This is a high-severity error that should not be ignored — running a water heater in an overheating condition can damage internal components, void your warranty, or create a safety hazard. Common causes include a blocked heat exchanger, insufficient water flow, a faulty thermistor, or a failed overheat cutoff sensor.