Rinnai Error Code 55: Rinnai Code 55 - False Fire Detection
How to Fix Rinnai Code 55
- Step 1: Immediately turn off the gas supply to the Rinnai unit at the gas shut-off valve.
- Step 2: Turn off the electrical power to the unit at the breaker.
- Step 3: Contact a qualified HVAC technician or Rinnai-certified service provider to inspect and repair the unit. Do not attempt to troubleshoot or repair the unit yourself.
How to Reset Rinnai Code 55
- 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 55 Mean?
Rinnai error code 55 indicates that the unit's flame sensor is detecting a flame when it shouldn't be. This can happen either before a call for heat, or after the unit is already off. This is a critical safety issue because it could mean that gas is leaking into the combustion chamber and creating a risk of uncontrolled ignition or carbon monoxide poisoning. It's important to address this immediately to prevent potential hazards and further damage to your Rinnai tankless water heater. Essentially, the unit 'thinks' it sees a flame when it shouldn't. The control board relies on the flame rod sensor to confirm the presence of a flame during normal operation. If the flame rod is sending the wrong signal, the control board can get confused and shut down the unit as a precaution.
Common Causes
- Defective flame sensor (rod)
- Faulty gas valve leaking gas into the combustion chamber
- Short circuit or wiring issue in the flame sensor circuit
- Problem with the main control board (PCB)
- Gas pressure too high
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Unit displays code 55 | Inspect the flame sensor rod for damage or carbon buildup | Rod is clean and undamaged |
| Flame sensor appears OK | Check the flame sensor wiring for shorts or loose connections | Wiring is intact and properly connected |
| Wiring is good | Measure the flame sensor microamp signal with a multimeter while the unit is running | Signal is within the manufacturer's specified range (typically 2-8 uA) |
| No obvious issues found | Check gas pressure with manometer | Gas pressure within specified range |
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 |
|---|---|---|---|
| Flame Rod Sensor | 273000014 | — | Find Part |
| Gas Valve | — | — | — |
| Main Control Board (PCB) | — | — | — |
Related Codes on Same Models
Other codes that affect the same Rinnai model families as 55.
| 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 |