Temperature sensor
Common error-code part. Confirm resistance and connector style.
Noritz NR111 Tankless Water Heater Error Codes
The Noritz NR111 is a high-capacity condensing tankless water heater (199,000 BTU/hr). Error codes display on the front panel LED/LCD. Codes can also be read via the Noritz app or EZ Link cascading controller.
NR111 Error Code Table
| Code | Fault Description | Common Cause | Action |
|---|---|---|---|
| 10 | Combustion issue | Vent blockage or combustion air fault | Inspect all vent terminations |
| 11 | Ignition failure | No gas, spark, or flame sensor | Check gas pressure and electrode |
| 12 | Flame loss mid-cycle | Unstable gas pressure | Check gas supply and regulator |
| 14 | Thermal fuse | Overheating event | Check heat exchanger flow and venting |
| 16 | High temp limit | Scale, low flow, or sensor fault | Flush HX, verify flow rate |
| 20 | Thermistor A | Outlet sensor failure | Replace outlet sensor |
| 21 | Thermistor B | Heat exchanger sensor fault | Replace HX sensor |
| 29 | Fan motor | Fan motor failure or wiring | Check fan RPM and amps |
| 31 | Combustion failure | Gas valve or electrode | Check gas valve output |
| 33 | Thermistor C | Inlet sensor fault | Replace inlet sensor |
| 52 | Gas valve modulation | Gas valve or PCB issue | Check valve coil resistance |
| 61 | Combustion fan | Fan motor failure | Check fan rotation and amps |
| 65 | Flow sensor | Low flow or debris | Check inlet screen and sensor |
| 71 | Gas valve error | Failed gas valve | Replace gas valve |
| 90 | Combustion problem | PCB or combustion air issue | Check combustion air and PCB |
Most Common NR111 Faults
Code 11 - Ignition Failure
NR111 requires minimum 3.5 in. w.c. gas pressure (natural gas) at the inlet. Verify full gas pressure with a manometer. Check igniter electrode condition and gap. Clean flame sensor rod with emery cloth.
Code 16 - High Temperature Limit
In hard water regions, scale builds rapidly in NR111’s stainless heat exchanger. The unit will overheat at lower flow rates as heat transfer degrades. Descale with citric acid solution annually. Also verify minimum flow rate (0.75 GPM).
Code 65 - Flow Sensor Fault
The NR111 flow sensor activates the burner when demand exceeds 0.75 GPM. A clogged inlet screen or debris from corroded pipes can restrict flow and prevent activation. Remove and clean the screen and sensor turbine.
Code 90 - Combustion Problem
Code 90 is logged when the unit detects repeated combustion failures not attributed to a specific sensor. Check combustion air supply, verify CO2 percentage in flue gas (should be 8-9.5% natural gas), and check PCB.
Parts Commonly Needed
| Part | Notes |
|---|---|
| Thermistor sensors | Check resistance vs. chart |
| Flow sensor | Clean turbine before replacing |
| Igniter/flame rod | Check gap: 3.5-4mm |
| Gas valve | Test coil resistance (8-12 ohm typical) |
| Fan motor | Match model voltage and RPM |
| Heat exchanger | Last resort - 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: Noritz NR111 units in cascade configurations (up to 16 units) can be monitored via the EZ Link controller. Fault codes for all units display on the controller - check here before visiting individual units.