Noritz Error Codes: Tankless Water Heater Fixes

Noritz Error Codes: Quick Reference

Noritz tankless water heaters display fault codes on the front-panel display or on a remote controller. Two-digit codes are standard across all Noritz product lines (NRCP, NRC, NR, NCC, EZ series). Most codes require pressing the RESET button after correcting the fault.

Most Common Codes

Safety Before You Start

Tankless water heaters run on natural gas or propane and involve combustion, exhaust venting, and hot water. Take these precautions before any troubleshooting.

• If you smell gas, do not attempt any troubleshooting. Leave the area, do not operate switches or the unit, and call your gas utility or 911 from outside the building.
• Turn off the unit’s power and close the gas shutoff valve before opening the cabinet or servicing gas connections.
• Let the unit cool before touching the heat exchanger, flue connections, or hot water piping. Combustion components and exhaust can stay hot well after shutdown.
• Descaling involves circulating diluted vinegar or a commercial descaler through the unit. Use the service valves as designed and avoid disconnecting water lines under pressure.
• Combustion air intake and exhaust vent work should follow the clearances and materials specified in the installation manual. Improper venting can allow flue gas, including carbon monoxide, into living or working spaces.
• If your gas or venting knowledge is limited, or the unit shows any sign of soot, discoloration around vent connections, or a persistent gas smell, stop and call a licensed technician.

Tools You Will Need

• Manometer for gas pressure testing at the test port
• Multimeter for thermistor resistance and continuity checks
• Small submersible pump and hose kit for descaling through the service valves
• White vinegar or a commercial tankless descaling solution
• Flashlight for inspecting the combustion air intake screen and vent termination
• Model and serial number recorded before ordering any parts

Most Common Codes

Code 11: Ignition Failure

Noritz could not ignite the burner.

1. Confirm the gas valve at the unit and the main shutoff are both fully open.
2. Check that the gas meter is active and no other large gas appliance is running at the same time, since a simultaneous draw can cause a pressure drop that prevents ignition.
3. On NRC and NRCP models, verify the combustion air intake screen is clear of debris, dust, or insect nests, since a restricted intake starves the burner of air needed for ignition.
4. Inspect the igniter for visible damage or carbon buildup, and clean gently if accessible per the service manual.
5. If gas supply, intake, and igniter all check out and ignition still fails, the gas valve or ignition control board may need professional testing.

Code 12: Flame Loss

The burner lit but flame went out mid-cycle. Intermittent gas pressure is the primary cause.

1. Test by running the unit and simultaneously measuring gas pressure at the test port with a manometer. Pressure should hold above 4 inches water column for natural gas under load; consult the installation manual for the exact spec for your gas type and model.
2. If pressure drops noticeably while firing, especially when other gas appliances turn on, contact the gas utility or a licensed gas fitter to evaluate the supply line sizing and regulator.
3. Check the flame sensor rod for carbon buildup or corrosion, since a fouled sensor can cause the control board to cut fuel even when the flame is present.
4. Inspect burner and heat exchanger surfaces for soot, which can also disrupt flame stability.

Code 16: Over-Temperature

Heat exchanger is running too hot.

1. On Noritz units installed in hard water regions, scale accumulation inside the copper or stainless heat exchanger is common after 3 to 5 years without maintenance. Noritz recommends an annual descaling flush regardless of whether codes have appeared.
2. Shut off gas and power, then connect a small pump to the service valve connections on the cold inlet and hot outlet.
3. Circulate white vinegar or a commercial descaling solution for about 45 minutes, following the volume and dwell time in the Noritz service manual for your model.
4. Flush thoroughly with clean water afterward to clear dissolved scale and any remaining solution.
5. Verify adequate water flow rate through the unit after descaling, since a restricted flow anywhere in the system, not just scale, can also trigger over-temperature protection.
6. If over-temperature recurs immediately after a full descale and flow verification, the heat exchanger itself or its thermistor may need professional evaluation.

Code 29: Condensate Drain Blocked

On condensing Noritz models (NCC, NRCP series), the condensate drain neutralizer collects acidic water condensed from combustion gases. When the neutralizer is clogged or the drain tube kinked, water backs up and trips the float switch.

1. Inspect the drain tube from the unit to the drain point for kinks, sags that trap water, or physical blockage, and correct the routing.
2. Open the neutralizer cartridge per the manual and check the limestone or neutralizing media. If the media has visibly dissolved away or turned to sludge, replace it rather than trying to top it off.
3. Clear any debris from the drain trap and confirm the float switch inside the neutralizer moves freely.
4. After clearing the blockage, run the unit and confirm condensate flows steadily to the drain without backing up.

Code 10: Abnormal Exhaust Temperature

The exhaust temperature sensor detected unusually high flue temperatures, indicating a scale-blocked heat exchanger or a venting restriction.

1. Check the exhaust vent pipe termination outside the building for blockage. Bird nests are common in horizontal through-wall vents, especially after periods of low use.
2. Inspect the vent run for any crushed sections, disconnected joints, or excessive length beyond the manufacturer’s rated maximum.
3. If the vent is clear and properly sized, flush the heat exchanger following the descaling procedure above, since scale buildup raises exhaust temperature even before it trips the over-temperature code.
4. If exhaust temperature stays high after clearing the vent and descaling, have a technician check the exhaust temperature sensor and combustion settings.

Code 90: Combustion Abnormality

The control board detected abnormal combustion, usually from an incorrect gas and air ratio.

1. Verify the unit’s configured gas type matches the actual supply. A unit set for natural gas but connected to LP, or vice versa, will run with an incorrect air-fuel ratio and can trigger this code along with unsafe combustion.
2. Do not attempt to adjust internal gas valve or combustion settings yourself. This requires a technician with combustion analysis equipment to verify safe operation.
3. Inspect the burner for visible damage, warping, or heavy soot as an indicator of a deeper combustion problem.
4. Treat code 90 as a stop-and-call-a-professional situation rather than a reset-and-continue code, since improper combustion can produce elevated carbon monoxide.

Parts Often Needed

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.

When to Call a Pro

Code 14 (thermal fuse), code 71 (gas valve solenoid), and code 90 (combustion abnormality) require certified technician service. Also call a professional when:

• You smell gas at any point, before, during, or after troubleshooting.
• Ignition failure, flame loss, or over-temperature persists after you have completed the checks above.
• The unit shows soot, scorching, or discoloration on the cabinet, vent connections, or nearby structure.
• You are not confident working with gas connections, venting, or combustion components.

Noritz recommends annual professional maintenance regardless of whether any codes appear, since scale buildup and sensor drift happen gradually and do not always trigger a fault before performance degrades.

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