Rinnai tankless descale flush kit
Use for code 16 or scale-related overheating after confirming the unit has isolation service valves.
$70-$170
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Rinnai Error Codes — Quick Reference
Rinnai tankless water heaters display fault codes as two-digit numbers on the front LED display. Rinnai uses codes across all major product lines (V, RU, RL, RH, RX, RUR series). Some codes are auto-reset; others require pressing the ON/OFF button to clear after correcting the fault.
| Code | Meaning | Quick Fix |
|---|---|---|
| 11 | Ignition failure | Check gas supply and gas valve |
| 12 | Flame failure | Clean flame sensor; check gas |
| 14 | Thermal fuse open | Unit overheated; check venting |
| 16 | Over-temperature cutoff | Flush heat exchanger; check flow |
| 25 | Condensate neutralizer blocked | Clean condensate trap |
| 31 | Inlet thermistor fault | Replace cold inlet thermistor |
| 32 | Outlet thermistor fault | Replace hot outlet thermistor |
| 33 | Heat exchanger thermistor fault | Replace HX thermistor |
| 61 | Combustion fan fault | Check fan motor |
| 65 | Water flow control valve fault | Check flow servo |
| 71 | Gas valve circuit fault | Check gas valve solenoid |
| 72 | Flame detected without gas call | Gas valve not closing |
| 79 | Combustion air supply fault | Check intake vent; fan motor |
Focused Parts Searches
Before ordering, match the water-heating part to the model number, fuel type, electrical rating, and failure symptom.
- Rinnai tankless descaling flush kit - use for scale and code 16 paths only when isolation service valves are installed.
- Rinnai condensate neutralizer kit - check condensing models when code 25 points to a blocked condensate path.
- Rinnai igniter electrode - clean and inspect ignition parts for code 11 before ordering.
- Rinnai tankless fan motor - price only after intake, exhaust, wiring, and model-specific fan checks.
Most Common Codes
Code 11: Ignition Failure
Rinnai couldn’t establish a flame on the first attempt. Check: (1) gas supply valve fully open, (2) no gas outage at the meter, (3) minimum gas pressure met (4” WC for natural gas at full fire). Also verify the unit isn’t in “vacation mode” — press ON/OFF to wake it.
On outdoor Rinnai units, code 11 can occur in freezing weather if the gas valve internals ice up — verify the unit’s freeze protection heater is working.
Code 12: Flame Failure During Operation
The flame went out during a draw. The most common cause is a drop in gas pressure during high-demand periods (simultaneous use of multiple gas appliances). Schedule a gas pressure test during peak demand. Another common cause: a dirty or corroded flame sensor rod — clean with fine steel wool.
Code 14: Thermal Fuse Open
The thermal fuse (a one-shot safety device) opened because the unit overheated. This is most often caused by inadequate combustion air (blocked intake) or recirculating exhaust gases (intake and exhaust too close together). The thermal fuse requires replacement by a technician — it’s a non-resettable device.
Code 16: Over-Temperature
The outlet water temperature exceeded the safety threshold. Causes: scale buildup in the heat exchanger (common in hard water areas), too-low flow rate (demand too small to dilute heat), or incorrect temperature set point. Descale the heat exchanger with white vinegar and verify flow rate is above the minimum activation flow (typically 0.5 GPM for Rinnai).
Code 25: Condensate Neutralizer Blocked
On Rinnai condensing models (RUR, RU157, etc.), the condensate neutralizer contains limestone chips to neutralize acidic condensate. When these chips dissolve over years, sediment clogs the drain. Remove and clean the neutralizer tray, replace the limestone media if depleted.
Code 61: Combustion Fan Fault
The fan isn’t running at the commanded speed. Check for obstructions in the air intake or exhaust vent pipes. If the fan runs but makes bearing noise, replacement is needed. On Rinnai V-series, the fan motor can be accessed from the front by removing the combustion chamber cover.
Code 72: Flame Without Gas Call
The flame sensor detects a flame when the unit isn’t calling for heat. This indicates a leaking gas valve — a safety issue. Turn off the gas supply to the unit and contact Rinnai service. Do not operate the unit.
When to Call a Pro
Code 14 (thermal fuse), code 72 (flame without call), and code 71 (gas valve fault) require licensed technician repair. The thermal fuse is a safety component that should never be bypassed or jumped.