🔍
Rinnai - ✅ Safe to Use

Rinnai - Error Code 34

Rinnai Water Heater error code 34: Combust air/exhaust thermistor fault.

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 34 Mean?

Rinnai Water Heater error code 34: Combust air/exhaust thermistor fault.

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 34 mean? ▼
Error code 34 on a Rinnai tankless water heater indicates: Combust air/exhaust thermistor fault. 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 34? ▼
Start by powering the unit off for 30 seconds and restarting. If error 34 returns, the underlying cause (combust air/exhaust thermistor fault) needs to be addressed. Check wiring connections and filters first before replacing components.
Is Rinnai error code 34 serious? ▼
It depends on the root cause. Some 34 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 →

Was this page helpful?

Rate the helpfulness of this page