Noritz Tankless Water Heater Error Codes — Complete Guide (NRC, NR, EZ Series)

Common Symptoms

• Error code displayed on Noritz front panel (Error 11, 12, 14, 16, 29, 31, 65, 90, or 99)
• No hot water — unit powers on but does not fire, error code on display
• Intermittent hot water — unit ignites then loses flame mid-shower, Error 12
• Limited or lukewarm hot water — heat exchanger overheat limiting output, Error 14
• No ignition on first attempt after long vacation or shutdown period — Error 11
• Flow sensor fault — unit does not activate even with adequate water flow, Error 65
• Condensate neutralizer alarm — Error 29 with orange LED on some models

Most Likely Causes

1. 1

   Error 11 — No Ignition (Most Common Noritz Field Code)

   Error 11 means the Noritz attempted ignition and did not detect a flame. This is the most common Noritz error code and has a clear diagnostic sequence. First: confirm gas supply — check whether other gas appliances in the home (gas range, gas dryer, gas furnace) are working normally. If nothing has gas, the supply has been interrupted — call the gas utility. Second: verify the gas shutoff valve at the unit is fully open (handle parallel to pipe). Third: check inlet gas pressure — natural gas requires 3.5 inches water column (WC) minimum at the unit under firing load; propane requires 8 inches WC. The NRC1111-DV draws up to 199,900 BTU/hr at full output — an undersized supply line can drop well below minimum pressure when the unit fires at full capacity. Fourth: clean the ignition electrode (NK-1665) — carbon deposits on the electrode tip or ceramic cracking prevents reliable spark. Inspect the electrode ceramic for cracks (replace assembly if cracked). Fifth: after long vacation periods, the gas supply line may have accumulated air — Error 11 after a 2-week absence is almost always air in the supply line; attempt 3–4 restart cycles to purge the air before diagnosing further.

2. 2

   Error 12 — Flame Failure During Operation

   Error 12 means the Noritz successfully ignited but lost the flame during the heating cycle. Different from Error 11 (failure to ignite): Error 12 means the flame established and then went out. Primary causes: gas pressure fluctuation during high-demand periods — check manifold pressure at the unit's inlet test port under full firing load (maintain 3.5 inches WC for natural gas throughout the cycle). Combustion air deficiency — inspect the vent termination cap and the full vent run for partial blockages; a partially blocked exhaust cap allows ignition but starves combustion at full BTU output. Flame sensor contamination — the flame sensing electrode (NK-1665 assembly includes both ignition and sensing rods) can accumulate carbon deposits that weaken the ionization signal; clean with fine steel wool. On outdoor models (NR981-OD), check for wind interference at the vent cap — strong crosswinds can extinguish the flame on outdoor units not shielded from direct wind.

3. 3

   Error 14 — Overtemperature (Scale Buildup or Low Flow Rate)

   Error 14 means the Noritz heat exchanger outlet temperature exceeded the safety threshold. In hard water areas (above 120 ppm), calcium and magnesium deposits accumulate in the heat exchanger tubes over 1–3 years, restricting flow and creating localized hot spots. The second cause of Error 14 is low water flow: if the water flow rate through the unit drops below the minimum activation threshold (0.5 GPM for most Noritz models), the unit continues firing but cannot transfer heat fast enough — the heat exchanger overheats. Check: flow restrictors on shower heads and aerators on faucets that are set below 0.5 GPM will not sustain firing. For scale buildup: perform the NorScale descaling procedure using Noritz NorScale descaler solution or white vinegar circulation through the isolation service valve ports. For flow issues: verify the minimum 0.5 GPM flow rate with an inline flow meter before descaling.

4. 4

   Error 16 — Overtemperature Bypass / Outlet Temperature Sensor

   Error 16 indicates the outlet water temperature sensor (NK-2060) has detected an abnormal temperature condition — either the sensor has failed (drifted out of calibration range) or an actual overtemperature bypass event has occurred. Error 16 is less common than Error 14 and more often indicates a sensor issue rather than active scale buildup. Diagnosis: with the unit off and cool, disconnect the NK-2060 temperature sensor connector and measure resistance with a multimeter. Noritz NTC thermistors read approximately 10,000Ω (10kΩ) at 77°F (25°C) — a reading significantly outside this range (OL = open circuit, or <1kΩ = shorted) indicates sensor failure. A sensor reading within range suggests the actual water temperature exceeded the safety setpoint — trace back to the same root causes as Error 14 (scale, low flow) before replacing the sensor.

5. 5

   Error 29 — Condensate Neutralizer Full (EZ111-COND Replacement Required)

   Error 29 appears on condensing Noritz models (NRC series) when the condensate neutralizer bead media has been exhausted. Noritz condensing units extract heat from the flue gas and produce acidic condensate (pH 3–5 from dissolved CO2). The condensate neutralizer (Noritz EZ111-COND or equivalent) contains limestone chips that raise the pH to approximately 6.5–7 before the condensate reaches the floor drain. When the limestone media is exhausted, the neutralizer no longer raises the pH — Error 29 triggers on models with a pH sensor, or the orange LED illuminates on models with a simple level sensor indicating the bead media needs replacement. Replace the entire EZ111-COND condensate neutralizer cartridge — do not attempt to refill with bulk limestone because particle size and flow path are engineered specifically for the EZ111-COND housing.

6. 6

   Error 31 — Inlet Water Temperature Sensor (NK-2050)

   Error 31 indicates the cold water inlet temperature sensor (NK-2050) has failed or is reporting a value outside the acceptable range. The inlet sensor measures incoming cold water temperature to calculate how much energy is needed to reach the target hot water setpoint. When this sensor fails, the unit cannot modulate the burner correctly and locks out as a safety measure. Diagnosis: disconnect the NK-2050 sensor connector and measure resistance at room temperature — should read approximately 10kΩ at 77°F. A reading of OL (open) = failed sensor, replace NK-2050. Also check the connector itself for corrosion or loose pins — sensor faults on older Noritz units are often connector corrosion rather than sensor failure. Clean connector pins with electrical contact cleaner before condemning the sensor.

7. 7

   Error 65 — Flow Sensor Fault (NK-2055, 0.4 GPM Minimum Activation)

   Error 65 indicates the water flow sensor (NK-2055) is reporting a flow rate below the minimum activation threshold or has failed mechanically. Noritz models activate at a minimum of 0.4 GPM water flow — the flow sensor is a turbine-type sensor inside the cold water inlet that must spin above a minimum RPM to signal the control board to fire the burner. Error 65 causes: (1) Water flow genuinely below 0.4 GPM — low-flow shower heads with flow restrictors set to 0.5 GPM or below will not activate the unit reliably. Remove any 0.5 GPM restrictors and use a 1.5–2.0 GPM minimum for tankless heater compatibility. (2) Flow sensor turbine wheel seized or jammed by debris — small particles of pipe scale or installation debris can jam the turbine. Remove the NK-2055 sensor from the cold inlet and inspect the turbine wheel for debris or calcium buildup. (3) Flow sensor failed — the NK-2055 turbine generates a pulse signal; a failed sensor produces no pulses regardless of flow. Replace the NK-2055 if the turbine spins freely but the error persists.

8. 8

   Error 90 / Error 99 — Control Board Fault (NK-5930)

   Error 90 indicates a combustion fan motor or fan circuit fault. Error 99 indicates a control board (PCB) internal fault. Both are high-cost diagnoses. For Error 90: inspect the combustion fan first — open the access panel and check that the fan blade is not obstructed and spins freely. Also inspect the vent termination for blockage that causes the fan to overload. Test the fan motor current with a clamp meter. If the fan spins freely, checks out electrically, and Error 90 persists, the fan speed sensor or the control board (NK-5930) has failed. For Error 99: the control board has detected an internal fault — this code indicates PCB failure and requires board replacement with NK-5930. Before ordering NK-5930: verify all other error codes have been cleared, all sensor connections are clean and secure, and the supply voltage to the unit is 120VAC ± 10% (110–132V). Register the unit with Noritz at noritz.com before ordering NK-5930 — warranty registration is required to access the 12-year heat exchanger warranty and may affect whether the board replacement is covered.

Quick DIY Checks

1. 1Error 11 — Step 1, verify gas supply and purge air after vacation: before touching any internal components, confirm gas supply. Turn on the gas range burner or another gas appliance in the home — does it light normally? If no gas appliances have gas, the gas supply to the home is interrupted — call the gas utility. If other appliances work but the Noritz does not fire, check the gas shutoff valve at the unit (quarter-turn ball valve on the supply line directly before the unit inlet — handle must be parallel to the pipe for open). If the Error 11 appeared after the unit was not used for 2 or more weeks (vacation, seasonal shutdown), the gas supply line likely has accumulated air from micro-leakage at the meter or regulator. Attempt 3–4 consecutive restart cycles (turn the unit off and on at the power switch, open a hot water tap to trigger each cycle) — this purges air from the supply line. Most post-vacation Error 11 faults clear after 2–4 restart cycles without any parts. If Error 11 persists after 4 cycles, proceed to gas pressure testing.
2. 2Error 11 — Step 2, check gas pressure at the manifold test port: gas pressure below the minimum under firing load is the most overlooked cause of Noritz Error 11 and Error 12. Use a low-pressure manometer (Magnehelic or digital U-tube, 0–14 inches WC range) at the unit's gas inlet test port. (a) Static pressure test: with the Noritz off and all gas appliances off, measure static inlet pressure — natural gas typical range is 5–10 inches WC. Below 3.5 inches WC static indicates a supply problem. (b) Dynamic pressure test under load: turn on the Noritz and open a hot water tap to trigger firing. Read the manometer during the full firing cycle. Natural gas dynamic pressure must stay above 3.5 inches WC throughout the cycle. For NRC1111-DV (199,900 BTU/hr max input), a 1/2-inch supply line that is adequate for a 60,000 BTU furnace will typically drop below minimum under Noritz full-fire load. Confirm supply line sizing with a licensed gas technician if pressure drops more than 0.5 inches WC during firing. Document the static and dynamic pressures before proceeding to igniter diagnosis.
3. 3Error 11 / Error 12 — Step 3, clean the ignition and flame sensing electrode (NK-1665): shut off the gas supply valve at the unit and close the cold water supply valve. Unplug the Noritz from the wall outlet. Remove the front access panel (typically 4–6 screws). Locate the burner assembly — the NK-1665 electrode assembly is a combined igniter/flame sensor mounted adjacent to the burner head. The assembly has two metal rod tips: one for ignition spark and one for ionization flame sensing. Inspect both rods: carbon deposits, oxidation, or a brown/black coating on the rod surface indicate contamination. Clean the metal rod surfaces with fine steel wool or 400-grit emery cloth — do not clean the ceramic insulator bodies. Also inspect the ceramic insulators for hairline cracks (a cracked ceramic allows current leakage, preventing reliable spark or ionization signal). If any ceramic shows cracking, order a replacement NK-1665 assembly. After cleaning, check the spark gap — should be 3–4 mm between the igniter rod tip and the nearest ground surface. Reinstall, restore gas and water, plug in, and attempt a hot water draw to test ignition.

Repair vs Replace

Recommended Tools & Parts

• Noritz Ignition / Flame Sensing Electrode — NK-1665

  Replacement combined ignition and flame sensing electrode assembly for Noritz NRC and NR series tankless water heaters. Fixes Error 11 and Error 12 when cleaning does not resolve the fault or when the ceramic insulator shows cracks. The NK-1665 includes both the igniter spark rod and the ionization sensing rod. Verify model-specific fitment before ordering — the NRC1111-DV and NRC98-DV may use different assemblies.

  $30–$60

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• Noritz Gas Valve — NK-2100

  Replacement gas valve for Noritz NRC and NR series. Controls gas flow to the burner assembly. Required when Error 11 persists after confirming adequate gas pressure, clean electrode, and functional flow sensor — indicating the valve is not opening. Verify natural gas vs. propane configuration and model-specific fitment before ordering.

  $130–$220

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• Noritz Flow Sensor — NK-2055

  Replacement turbine-type cold water inlet flow sensor for Noritz NRC and NR series. Fixes Error 65 when the turbine is seized with debris or scale, or when the sensor has failed electronically. Minimum activation flow is 0.4 GPM on most Noritz models — confirm adequate fixture flow rate before replacing.

  $25–$55

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• Noritz Condensate Neutralizer — EZ111-COND

  Replacement condensate neutralizer cartridge for Noritz NRC condensing series. Contains limestone bead media that raises condensate pH from 3–5 to approximately 6.5–7 before discharge to the floor drain. Required when Error 29 appears — replace the entire EZ111-COND cartridge, do not refill with bulk limestone. Annual replacement recommended on high-use installations.

  $25–$50

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• NorScale Descaler Kit

  Noritz-recommended descaling solution for NRC and NR series heat exchanger maintenance. Dissolves calcium carbonate scale from heat exchanger coils for Error 14 treatment and annual preventive maintenance. More effective on heavy carbonate scale than white vinegar. Includes mixing instructions and safety data sheet.

  $25–$50

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• Noritz Control Board — NK-5930

  Replacement PCB control board for Noritz NRC and NR series. Required for Error 99 PCB fault. Register unit at noritz.com before ordering — warranty registration may affect coverage. Confirm supply voltage (120VAC) and inspect all sensor connectors before condemning the board. Verify model-specific part number — NRC1111-DV, NRC98-DV, and NRC661-DV may use different board variants.

  $180–$300

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Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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