Temperature sensor
Common error-code part. Confirm resistance and connector style.
Rinnai I120CN Tankless Water Heater Error Codes
The Rinnai I120CN is a commercial condensing tankless water heater rated at 120,000 BTU/hr. Error codes display on the unit’s front panel LCD. Codes can also be accessed via the Rinnai Control-R Wi-Fi module or Rinnai commercial controller.
I120CN Error Code Table
| Code | Fault Description | Common Cause | Action |
|---|---|---|---|
| 10 | Combustion air/exhaust fault | Blocked vent or incorrect venting | Inspect all vent terminations |
| 11 | Ignition failure | No gas or failed igniter | Check gas pressure and igniter |
| 12 | Flame loss | Gas pressure instability | Check gas supply line pressure |
| 14 | Thermal fuse blown | Overheating | Inspect heat exchanger and venting |
| 16 | Overheating (high temp) | Lime scale or low flow | Flush heat exchanger |
| 20 | Thermistor fault | Outlet sensor failure | Check sensor resistance |
| 25 | Condensate neutralizer full | Full condensate trap | Clear condensate drain |
| 29 | Fan motor fault | Failed combustion fan | Check fan amps and connections |
| 31 | Combustion failure | Gas pressure or electrode issue | Check gas and electrode gap |
| 32 | Outlet thermistor fault | Sensor open or shorted | Replace outlet sensor |
| 33 | Inlet thermistor fault | Sensor open or shorted | Replace inlet sensor |
| 52 | Modulation fault | Gas valve or control board | Check gas valve operation |
| 61 | Combustion fan fault | Fan motor failure | Check fan rotation and amps |
| 65 | Flow sensor fault | Low flow or failed sensor | Check minimum flow rate (0.6 GPM) |
Most Common I120CN Faults
Code 11 - Ignition Failure
Check gas pressure at the unit inlet (7-10.5 in. w.c. natural gas for commercial models). Clean or replace the igniter electrode - check gap (3.5-4mm). Clean flame sensor rod.
Code 16 - Overheating
The I120CN monitors outlet temperature continuously. In hard water areas, scale accumulation in the heat exchanger reduces flow and causes overheating. Flush annually with commercial descaler. Also check for insufficient flow (minimum 0.75 GPM for I120CN).
Code 65 - Flow Sensor Fault
Commercial units require minimum flow to activate. Check that the cold water inlet screen is clean. Verify the flow sensor turbine spins freely - debris from system flush can lock the turbine.
Code 25 - Condensate
The I120CN is a condensing unit. The condensate neutralizer requires annual replacement. A clogged neutralizer causes the unit to lock out on fault 25. Replace the neutralizer media annually.
Parts Commonly Needed
| Part | Notes |
|---|---|
| Condensate neutralizer media | Annual replacement required |
| Inlet/outlet thermistors | Check resistance vs. temperature chart |
| Igniter electrode | Check gap specification |
| Fan motor | Commercial voltage - match model |
| Flow sensor | Turbine type - clean before replacing |
| Heat exchanger | Expensive - descale first |
Need Replacement Parts?
Before ordering, match the water-heating part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Pro tip: The Rinnai I120CN supports up to 24 units in a cascading system. When diagnosing a cascade, check the system controller for which unit triggered the fault - not all units display active codes simultaneously.