Rinnai Water Heater Error Code 35: How to Fix It
Medium 30-60 minutes Medium Severity
Verified June 2026
- Error Code
- 35
- Brand
- Rinnai
- Product Type
- water_heater
- Severity
- Medium
- DIY Difficulty
- Medium
- Estimated Fix Time
- 30-60 minutes
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Tools You'll Need
- Multi-meter
- Phillips screwdriver
- Vacuum cleaner with crevice tool
- Gloves
How to Fix Error Code 35
-
Safety First: Power Off
Risk of electric shock. Ensure power is completely off before proceeding. -
Check Air Intake and Exhaust Vents
-
Inspect the Fan Motor
Be careful of sharp edges inside the unit. Wear gloves if necessary. -
Test the Thermal Fuse 4
Do not bypass the fuse. Replace with an identical thermal fuse rated for your model. -
Replace the Thermal Fuse (if needed)
Ensure the replacement fuse matches the specifications (temperature rating and amperage). -
Reassemble and Test
Monitor the unit for a few minutes to ensure proper operation. If the error reoccurs, turn off the system and call a technician.
Parts You May Need
Thermal fuse 4 (compatible with Rinnai tankless water heater)
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Fan motor (if faulty)
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Thermal fuse 4 (compatible with Rinnai tankless water heater)
Check Price on Amazon
Fan motor (if faulty)
Check Price on Amazon
Thermal fuse 4 (compatible with Rinnai tankless water heater)
Check Price on Amazon
Fan motor (if faulty)
Check Price on Amazon
Thermal fuse 4 (compatible with Rinnai tankless water heater)
Check Price on Amazon
Fan motor (if faulty)
Check Price on Amazon
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When to Call a Professional
If the error returns after replacing the thermal fuse, or if you have difficulty accessing the fan motor or heat exchanger, call a qualified HVAC technician. Persistent overheating may indicate a deeper issue like a gas valve problem or heat exchanger failure.Frequently Asked Questions
What does error code 35 mean on a Rinnai water heater?
Error code 35 means thermal fuse 4 has blown. This is a safety device that trips when the unit overheats.
How do I reset a Rinnai water heater after error 35?
First, fix the cause of overheating (e.g., clean vents, replace fan). Then, replace the blown thermal fuse if needed. Restore power and the error should clear. No manual reset button exists.
Can I bypass the thermal fuse on a Rinnai?
No. Bypassing the thermal fuse is dangerous and can cause fire or damage. Always replace with the correct part.
How much does it cost to fix error 35 on a Rinnai?
If DIY, a thermal fuse costs about $5-$20. If you hire a professional, expect $150-$300 for diagnosis and repair.
Why does my Rinnai keep blowing thermal fuses?
Recurring blown fuses indicate an underlying problem like restricted airflow, a failing fan motor, or a blocked heat exchanger. Have a technician inspect the unit.