Rinnai - ⛔ Do Not Use

Rinnai - Error Code 33

Q: "What does Rinnai Water Heater error code 33 mean?"

"Error code 33 on a Rinnai tankless water heater indicates: Exhaust/flue thermistor fault. The unit has detected this condition and has limited or stopped operation to prevent further damage."

Q: "How do I fix Rinnai Water Heater error code 33?"

"Start by powering the unit off for 30 seconds and restarting. If error 33 returns, the underlying cause (exhaust/flue thermistor fault) needs to be addressed. Check wiring connections and filters first before replacing components."

Q: "Is Rinnai error code 33 serious?"

"It depends on the root cause. Some 33 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."

Rinnai Water Heater error code 33: Exhaust/flue thermistor fault.

Is it safe?

⛔ No — stop using

Do NOT operate — potential gas or CO hazard. Ventilate the area and call a technician immediately.

Can I fix it?

Technician Required

Repair cost

Pro: $150–$600

⏱ 1–3 hours (pro)

What Does Error Code 33 Mean?

Rinnai Water Heater error code 33: Exhaust/flue thermistor fault.

Part that typically fails: Gas valve / igniter / heat exchanger

Do NOT operate — potential gas or CO hazard. Ventilate the area and call a technician immediately.

Symptoms You May Notice

⚠️ Water temperature fluctuating
⚠️ Unit running constantly
⚠️ Error on control panel

What the Technician Will Do

🔧 Professional repair required. Do not attempt DIY — this repair requires specialized tools or certification.

1 Check your owner's manual for model-specific guidance on error code reset procedures
2 Test the temperature sensor with a multimeter — replace if reading is outside spec
3 Inspect sensor wiring harness for damage or loose connections
4 If the error persists after reset and basic checks, contact a qualified technician

⚡ 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 33 mean? ▼

Error code 33 on a Rinnai tankless water heater indicates: Exhaust/flue 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 33? ▼

Start by powering the unit off for 30 seconds and restarting. If error 33 returns, the underlying cause (exhaust/flue thermistor fault) needs to be addressed. Check wiring connections and filters first before replacing components.

Is Rinnai error code 33 serious? ▼

It depends on the root cause. Some 33 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

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