Navien Water Heater Error Code 027: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
027
Brand
Navien
Product Type
water_heater
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code 027 on your Navien tankless water heater means the cold water inlet thermistor is faulty or has a wiring issue. This sensor monitors incoming water temperature; when it fails, the heater cannot operate properly. Follow these steps to diagnose and fix the problem.
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Tools You'll Need

How to Fix Error Code 027

  1. Safety First: Power Down

    Always turn off power and gas before servicing to avoid electric shock or gas leaks.

  2. Locate the Cold Water Inlet Thermistor

  3. Inspect Wiring Connections

  4. Test the Thermistor with a Multimeter

    Ensure the multimeter is set correctly to avoid damaging the sensor.

  5. Replace the Thermistor if Faulty

    Use only genuine Navien replacement parts to ensure proper fit and function.

  6. Reassemble and Test

Parts You May Need

Cold water inlet thermistor
Check Price on Amazon
Cold water inlet thermistor
Check Price on Amazon
Cold water inlet thermistor
Check Price on Amazon
Cold water inlet thermistor
Check Price on Amazon
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When to Call a Professional

If the error persists after replacing the thermistor, the issue may be with the control board or wiring harness. Contact a qualified technician for further diagnosis.

Frequently Asked Questions

What does Navien error code 027 mean?
It indicates a fault with the cold water inlet thermistor, which measures incoming water temperature. The heater may shut down to prevent improper operation.
Can I still use hot water with error code 027?
No, the heater will not operate correctly and may not provide hot water. You need to fix the error before using.
How do I test a Navien thermistor?
Use a multimeter set to resistance. At room temperature, the thermistor should read around 10,000 ohms. Compare to the specification for your model.
Where can I buy a replacement thermistor for Navien?
You can purchase them from authorized Navien dealers, online retailers like Amazon, or plumbing supply stores.
Is it safe to replace the thermistor myself?
Yes, if you follow safety precautions like turning off power and gas. However, if you are uncomfortable with electrical testing, hire a professional.

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