Rinnai Error Code 63: Rinnai Code 63 - Excessive Temperature Rise
How to Fix Rinnai Code 63
- Step 1: Check that all hot water taps are fully closed. A dripping faucet can cause the unit to cycle and potentially trigger the error.
- Step 2: Try resetting the unit by turning off the power at the breaker for 30 seconds, then turn it back on. This may clear a temporary fault.
- Step 3: If the error persists after resetting, contact a qualified HVAC technician experienced with Rinnai tankless water heaters for professional diagnosis and repair.
How to Reset Rinnai Code 63
- 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 63 Mean?
Rinnai error code 63 indicates an excessive temperature rise within the heat exchanger. The unit's sensors detected the water temperature increasing too quickly, triggering a safety shutdown. This usually means the burner is firing too intensely for the amount of water flowing through the unit. It's a protective measure to prevent scalding, damage to the unit, and potential steam explosions. The unit will lock out and display this error until the problem is resolved. This issue affects the burner assembly, water flow regulation, and temperature sensors within your Rinnai tankless water heater. Ignoring this error can lead to further component damage or even a dangerous situation.
Common Causes
- Scale buildup inside the heat exchanger restricting water flow.
- Faulty flow sensor not accurately measuring water flow rate.
- Defective thermistor providing incorrect temperature readings to the control board.
- Gas valve malfunction causing excessive gas flow to the burner.
- Incorrect gas pressure supplied to the unit.
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Unit displays code 63 | Measure incoming gas pressure at the gas valve with a manometer | Within Rinnai's specified range (typically 4-7" WC for natural gas, 8-11" WC for propane) |
| Gas pressure is within range | Check thermistor resistance at the control board connector with a multimeter | Resistance should match the temperature/resistance chart in the Rinnai service manual |
| Thermistor checks good | Inspect the heat exchanger for scale buildup using a borescope | Minimal to no scale present |
| No scale is present | Verify the flow sensor signal to the control board with a multimeter while water is flowing | Signal voltage or frequency should correspond to the flow rate according to the Rinnai service manual |
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 |
|---|---|---|---|
| Flow Sensor | 804000047 | — | Find Part |
| Thermistor | 804000083 | — | Find Part |
| Gas Valve | — | — | — |
Related Codes on Same Models
Other codes that affect the same Rinnai model families as 63.
| 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 |