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Rinnai - ✅ Safe to Use

Rinnai - Error Code 31

Rinnai Water Heater error code 31: Thermistor open circuit.

Last reviewed: Last updated:

Methodology: We combine OEM HVAC documentation with field repair patterns, then review for safety-first troubleshooting.

Sources: HVAC manufacturer documentation, installation/service manuals, and technician-reported repair patterns.

Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.

Is it safe?
✅ Safe temporarily
Safe to use on cold settings temporarily. Heating element failure is a common DIY repair.
Can I fix it?
DIY Possible
Tools: Multimeter, Screwdriver set, Nut driver
Repair cost
DIY: $20–$100 (element or thermistor)
Pro: $100–$300
⏱ 30–60 min

What Does Error Code 31 Mean?

Rinnai Water Heater error code 31: Thermistor open circuit.

Part that typically fails: Heating element / thermal fuse / thermistor

Safe to use on cold settings temporarily. Heating element failure is a common DIY repair.

Symptoms You May Notice

Troubleshooting Steps

  1. 1 Check your owner's manual for model-specific guidance on error code reset procedures
  2. 2 Test the temperature sensor with a multimeter — replace if reading is outside spec
  3. 3 Inspect sensor wiring harness for damage or loose connections
  4. 4 If the error persists after reset and basic checks, contact a qualified technician
🛠️ Tools needed: Multimeter, Screwdriver set, Nut driver · Time: 30–60 min
⚡ Quick tip: Always try a full power reset first — turn the unit off at the breaker, wait 30 seconds, restore power.

Frequently Asked Questions

What does Rinnai Water Heater error code 31 mean? ▼
Error code 31 on a Rinnai tankless water heater indicates: Thermistor open circuit. The unit has detected this condition and has limited or stopped operation to prevent further damage.
How do I fix Rinnai Water Heater error code 31? ▼
Start by powering the unit off for 30 seconds and restarting. If error 31 returns, the underlying cause (thermistor open circuit) needs to be addressed. Check wiring connections and filters first before replacing components.
Is Rinnai error code 31 serious? ▼
It depends on the root cause. Some 31 errors resolve with a reset. Others indicate a failed component that requires professional repair. Don't continue operating with this error — it can lead to further damage.

More Rinnai - Error Codes

All Rinnai - codes → All Rinnai HVAC codes →

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