Navien Tankless Water Heater Error Code 029: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
029
Brand
Navien
Product Type
water_heater
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code 029 on your Navien tankless water heater indicates a fault with the hot water outlet thermistor, a sensor that monitors the outgoing water temperature. This issue can cause the unit to shut down or operate erratically. Follow the steps below to diagnose and resolve the problem.
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Tools You'll Need

How to Fix Error Code 029

  1. Safety First: Power Off and Shut Water Supply

    Always shut off gas and power before working on the water heater to avoid electric shock or gas leaks.

  2. Access the Hot Water Outlet Thermistor

  3. Check the Thermistor Connection

  4. Test the Thermistor Resistance

    Handle the multimeter probes carefully to avoid shorting circuits.

  5. Replace the Faulty Thermistor

    Ensure the replacement part matches the original specifications.

  6. Restore Power and Test

    If the error persists after replacement, there may be a main board issue. Contact a professional technician.

Parts You May Need

Hot water outlet thermistor
Check Price on Amazon
Hot water outlet thermistor
Check Price on Amazon
Hot water outlet thermistor
Check Price on Amazon
Hot water outlet thermistor
Check Price on Amazon
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When to Call a Professional

If you are uncomfortable working with gas or electrical components, or if the error returns after replacing the thermistor, call a certified HVAC technician. Main board failures require professional diagnosis and repair.

Frequently Asked Questions

What is Navien error code 029?
Error code 029 indicates a fault with the hot water outlet thermistor on your Navien tankless water heater. This sensor measures the outgoing water temperature; when it fails, the heater may shut down.
How much does it cost to fix Navien error code 029?
The cost is mainly the part (thermistor), around $20-$50. If you hire a professional, labor may add $100-$200. DIY saves labor costs.
Can I still use hot water with error code 029?
The heater may not operate or may shut off frequently. It's best to fix the error to avoid potential damage. Running the unit with a faulty thermistor can lead to overheating.
Where is the hot water outlet thermistor on a Navien water heater?
It is attached to the hot water outlet pipe on the top of the unit, near the heat exchanger. It looks like a small sensor with two wires.
What causes the hot water outlet thermistor to fail?
Common causes include normal wear and tear, electrical surges, or scale buildup. Water quality issues can also accelerate sensor failure.

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