Rinnai Error Code 33: Heat Exchanger Thermistor
Warning: Your Rinnai water heater is locked out due to a potential heat exchanger issue. It's safe to troubleshoot, but don't attempt to fix it yourself.
How to Fix Rinnai Code 33
- Check if your water heater is receiving power. The display should light up when you turn on the power switch.
- Try resetting the water heater by turning off the power at the circuit breaker, waiting 30 seconds, then turning it back on.
- If the error persists, do not attempt to fix it yourself. Call a professional HVAC technician.
How to Reset Rinnai Code 33
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Rinnai Error Code 33 Mean?
Error code 33 on your Rinnai water heater indicates a problem with the heat exchanger thermistor. This sensor monitors the temperature of the heat exchanger and helps regulate the water temperature. If it's not working properly, your water heater may not heat water or could shut down to prevent overheating. This is a yellow hazard level because it's safe to troubleshoot, but you should call a professional for repairs.
Common Causes
- Faulty heat exchanger thermistor
- Wiring issue to the thermistor
- Corroded or damaged heat exchanger
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Water heater is not heating water or displaying error code 33 | Measure the resistance of the heat exchanger thermistor using a multimeter. It should be between 10,000 to 100,000 ohms, depending on the temperature. | Resistance within the specified range for the current temperature |
| Thermistor resistance is out of range | Inspect the wiring to the thermistor for any damage or corrosion. | No damage or corrosion, and wires are securely connected |
Applicable Rinnai Models
- CU(gas)
- HE(dual_fuel)
- HE++ Series(gas)
- I-SERIES(gas)
- NCB(gas)
- NPE(gas)
- RE(gas)
- REP(gas)
- RL(gas)
- RU(gas)
- RUCS(gas)
- RX(gas)
- RXP(gas)
- Rinnai NCB Series(gas)
- Rinnai NPE Series(gas)
- Rinnai R Series(gas)
- Rinnai RL Series(natural_gas)
- Rinnai RU Series(natural_gas)
- Rinnai RUR Series(gas)
- Rinnai VSP(gas)
- V(gas)
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Heat Exchanger Thermistor | RIN-102565600 | — | Find Part |
| Wiring Harness | RIN-102565700 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Rinnai model families as 33.
| Code | Description | Severity |
|---|---|---|
| 02 | Stagnant Water Detection | Warning |
| 10 | Air Supply/Exhaust Blockage | Warning |
| 11 | No Ignition | Warning |
| 12 | Flame Failure | Warning |
| 14 | Thermal Fuse | Warning |
| 16 | Over-Temperature | Warning |
| 19 | Electrical Grounding | Warning |
| 25 | Condensate Overflow | Warning |
| 29 | Condensate Neutralizer | Warning |
| 31 | Inlet Thermistor Failure | Warning |