When your tankless water heater flashes an error code, you don't need to panic or immediately call a plumber. Most common error codes point to fixable problems: a flame rod that needs cleaning, a gas valve that isn't fully open, or a vent pipe that accumulated debris. This guide decodes the most frequent error codes across Rinnai, Navien, and Noritz tankless units and walks you through the fixes homeowners can safely handle themselves.
Rinnai Tankless Error Codes
Rinnai tankless water heaters use numeric codes that appear on the unit's digital display. Below are the most common codes and their meaning:
| Code | Meaning | Most Common Cause | Typical Fix |
|---|---|---|---|
| 11 | No ignition | Gas supply off, igniter dirty, or flame rod contaminated | Verify gas valve open, clean flame rod, inspect igniter |
| 12 | Flame failure | Gas pressure too low, flame rod needs cleaning | Check inlet gas pressure (7" WC NG, 10" WC LP), clean flame rod |
| 14 | Overheating | Scale buildup in heat exchanger, flow restriction | Descale heat exchanger, check inlet filter |
| 16 | Over temperature | Outlet thermistor failure or severe scale buildup | Professional service required (thermistor replacement) |
| 25 | Solenoid valve failure | Control board or valve issue | Call technician (gas valve or board replacement) |
| 79 | Blocked vent | Vent pipe obstruction or icing in cold climates | Inspect vent termination for blockages, clear ice |
Rinnai Error Code 11: No Ignition
Error 11 is the most common Rinnai fault. It means the unit attempted to ignite gas but failed. Start by checking that the gas valve (on the supply line to the heater) is fully open. If the valve is open and you have gas service to other appliances, the igniter or flame rod likely needs attention. Do not attempt to disassemble the combustion chamber unless you are comfortable working with gas appliances. For units over 3 years old, carbon buildup on the igniter or flame rod is the usual culprit. Cleaning the flame rod with fine-grit sandpaper and checking the igniter for cracks often resolves error 11. If the error persists, call a licensed technician to test gas pressure at the unit and inspect the gas valve.
Rinnai Error Code 12: Flame Failure
Code 12 appears when the unit ignites initially but loses flame during operation. This usually indicates insufficient gas pressure or a flame rod that cannot reliably sense the flame. Measure inlet gas pressure with a manometer: natural gas should read 7 inches water column, propane 10-11 inches. If pressure is low, contact your gas utility (for NG) or propane supplier. If pressure is correct, remove and clean the flame rod. Some Rinnai models also throw code 12 when the combustion fan is failing; listen for unusual fan noise or reduced airflow.
Rinnai Error Code 14: Overheating
Error 14 signals that outlet water temperature exceeded the safety limit. The two most common causes are scale buildup inside the heat exchanger (which restricts flow and concentrates heat) and a clogged inlet filter. Turn off the unit and let it cool. Remove and rinse the inlet filter. If the filter was clean or the error reappears after filter cleaning, the heat exchanger likely needs descaling. Use a descaling pump and tankless-specific descaling solution (citric or phosphoric acid-based) per the Rinnai maintenance manual. Hard water areas should descale annually to prevent error 14.
Navien Tankless Error Codes
Navien units use alphanumeric error codes (E-series) displayed on the front panel or remote controller. The most frequent codes:
| Code | Meaning | Most Common Cause | Typical Fix |
|---|---|---|---|
| E003 | Ignition failure | Gas supply, igniter, or flame rod issue | Verify gas on, clean flame rod, check igniter |
| E012 | Flame loss | Low gas pressure or flame rod contamination | Check gas pressure (7" WC NG, 10" WC LP), clean flame rod |
| E027 | Abnormal flow sensor | Scale buildup or faulty flow sensor | Descale unit, inspect flow sensor for debris |
| E030 | Exhaust overheating | Blocked vent or insufficient combustion air | Inspect vent for obstructions, verify clearances |
| E436 | Outlet overheat sensor | Scale in heat exchanger or sensor failure | Descale heat exchanger or replace sensor (call tech) |
| E515 | Water leak detected | Internal leak or condensate drain backup | Check condensate drain, inspect heat exchanger (call tech if leak confirmed) |
Navien Error Code E003: Ignition Failure
E003 is Navien's equivalent of Rinnai's code 11. The unit tried to light but failed. First, confirm gas supply. Check that the manual gas shutoff valve upstream of the heater is open and that your gas meter is running (indicating service is active). If you smell gas at any point, turn off the gas supply immediately and call your gas utility. Assuming gas supply is good, remove the front cover and locate the flame rod (a thin metal rod extending into the burner area). Remove it carefully and clean with fine sandpaper or a soft cloth. Inspect the igniter (a ceramic component near the burner) for cracks. Hairline cracks in the igniter prevent reliable spark and require igniter replacement.
Navien Error Code E012: Flame Loss
E012 appears when the unit successfully ignites but then loses flame during a hot water draw. This points to borderline gas pressure or a flame rod that intermittently loses conductivity. Measure gas pressure at the unit with a manometer during a hot water draw (when the burner is firing). Natural gas should hold steady at 7 inches water column; propane 10-11 inches. Pressure dropping below 5 inches (NG) during firing indicates an undersized gas line or a regulator problem. If pressure is stable, clean the flame rod and verify the ground wire connection on the rod is tight.
Navien Error Code E027: Abnormal Flow Sensor
E027 indicates the flow sensor is reading erratic or out-of-range values. Scale buildup in the heat exchanger restricts flow and causes turbulent readings. Descale the unit with a flush kit. If descaling does not clear E027, the flow sensor itself may be fouled or failing. The flow sensor is typically accessible by removing the water inlet assembly; inspect for debris or mineral buildup on the sensor paddle. Rinse thoroughly. If the sensor is damaged or E027 persists, the sensor requires replacement (a job for a technician familiar with Navien units).
Noritz Tankless Error Codes
Noritz uses numeric codes similar to Rinnai, displayed on the unit's front panel LED:
| Code | Meaning | Most Common Cause | Typical Fix |
|---|---|---|---|
| 11 | Ignition failure | Gas off, igniter, or flame rod issue | Verify gas on, clean flame rod, check igniter |
| 12 | Flame failure | Gas pressure low, flame rod dirty | Test gas pressure, clean flame rod |
| 29 | Combustion abnormality | Blocked vent, insufficient air, or flame rod contamination | Inspect vent for blockages, verify air supply clearances |
| 66 | Bypass servo error | Bypass valve motor failure (indoor units) | Call technician (motor or control board replacement) |
| 90 | Combustion abnormality (90+ series) | Vent blockage or air supply restriction | Clear vent, confirm combustion air intake not blocked |
| 99 | Blocked vent | Vent pipe obstruction or incorrect termination | Inspect vent run, clear blockages, verify termination meets code |
Noritz Error Code 11 and 12: Ignition and Flame Failures
Noritz codes 11 and 12 mirror Rinnai codes of the same number. Code 11 means no ignition occurred; code 12 means ignition succeeded but flame was lost. Troubleshooting steps are identical: verify gas supply, check inlet gas pressure, and clean the flame rod. Noritz flame rods are held in place with a single screw; remove, clean with fine sandpaper, and reinstall. Check that the ground wire on the flame rod has continuity to the unit chassis. A loose or corroded ground prevents flame sensing and causes repeated error 11 or 12.
Noritz Error Code 29: Combustion Abnormality
Error 29 signals abnormal combustion, which can mean incomplete combustion, flame rollout, or unstable flame. The most common cause is blocked or restricted venting. Walk outside and inspect the vent termination. Look for bird nests, wasp nests, lint buildup (if the vent is near a dryer exhaust), or ice accumulation in winter. Remove any blockages. Next, verify that the vent run complies with the installation manual: no excessive length, correct diameter pipe, and proper termination height above grade. If venting appears clear, the combustion fan may be failing (reduced RPM or bearing noise). A failing fan cannot pull enough air through the burner, causing incomplete combustion and error 29. Fan replacement requires a technician.
Noritz Error Code 66: Bypass Servo Error
Code 66 appears on Noritz indoor condensing models (NC and NRC series) and indicates the bypass servo motor is not responding correctly. The bypass valve modulates hot water mixing to maintain outlet temperature. If the servo motor stalls or the control board cannot confirm valve position, the unit throws error 66. This is not a DIY fix. Power-cycle the unit once (turn off the circuit breaker for 30 seconds, then restore power). If error 66 reappears immediately, call a Noritz service technician. The servo motor or control board requires replacement.
Noritz Error Code 99: Blocked Vent
Code 99 is a dedicated blocked-vent fault. The unit detected excessive back pressure in the vent system. Inspect the entire vent run from the unit to the termination. Check for: - Crushed or kinked flex pipe (if flex vent was used) - Excessive horizontal run length (consult the manual for max length per pipe diameter) - Improper termination (too close to windows, soffits, or air intakes) - Icing at the termination in freezing weather (more common with condensing models that exhaust cooler gases)
If the vent run is correct and clear, the pressure switch or its sensing tube may be clogged with condensate residue. This check requires removing the unit's cover and inspecting the pressure switch tubing. Unless you are experienced with HVAC diagnostics, call a technician for pressure switch service.
When to Call a Professional
You can safely troubleshoot and resolve many tankless error codes yourself: verifying gas supply, cleaning flame rods, checking venting, and descaling heat exchangers. However, certain faults require professional service:
- Persistent ignition failures after basic troubleshooting: If gas is on, flame rod is clean, and the error reappears, the igniter, gas valve, or control board may be faulty.
- Gas smell at any time: Turn off the gas supply and call your gas utility immediately. Do not attempt to troubleshoot further.
- Error codes involving the heat exchanger sensor or thermistor: These components require multimeter testing and precise replacement. Misdiagnosis can lead to unsafe operation or unit damage.
- Repeated overheat errors after descaling: The heat exchanger may have severe scale deposits that require professional descaling equipment, or a thermistor/sensor may have failed.
- Control board or valve errors (Rinnai 25, Noritz 66): These faults indicate electrical or mechanical component failure beyond typical homeowner tools.
- Multiple unrelated error codes in quick succession: This pattern often indicates control board failure or a wiring fault. A technician with a multimeter and the service manual is required.
When you call a technician, provide the exact error code and note any patterns (e.g., "error 12 appears only during cold weather" or "error E027 started after a power outage"). This speeds diagnosis and reduces service call time.
Recommended Tankless Models (Based on Reliability)
If you're evaluating tankless models based on error frequency and ease of service, the following units have the best track records for low maintenance and straightforward troubleshooting:
Rinnai RU199iN Ultra Series (Natural Gas, Indoor)
The Rinnai RU199iN is a workhorse condensing unit rated 11 GPM at 35°F rise. It uses Rinnai's proven heat exchanger design and has accessible flame rod and igniter service points. The control board logs error history, which helps technicians diagnose intermittent faults. Condensing efficiency (0.96 UEF) reduces operating cost in high-use households. The unit's large burner and generous heat exchanger volume make it less prone to scale-induced overheat errors compared to compact competitors.
Navien NPE-240A2 (Natural Gas, Indoor)
The Navien NPE-240A2 balances affordability and performance. Rated 10 GPM, it covers 3-4 bathroom homes. Navien's recirculation compatibility (built-in pump and buffer tank in the NPE-A2 series) reduces the delay-at-fixture problem common with tankless. The unit's error codes are well-documented in the homeowner manual, and Navien's flame rod is easily accessible. The stainless steel heat exchanger resists corrosion better than copper competitors in areas with aggressive water chemistry.
Noritz NRC111-DV-NG (Natural Gas, Indoor Condensing)
The Noritz NRC111-DV-NG is a mid-capacity (11.1 GPM max) indoor direct-vent condensing model. It runs quieter than non-condensing competitors and vents with PVC, reducing installation cost. Noritz units have a reputation for long service life (15-20 years with maintenance). The NRC111's error code display is straightforward, and the unit's modular design allows technicians to replace components without full disassembly.
Final Thoughts
Error codes on tankless water heaters are diagnostic tools, not death sentences. Most common codes (11, 12, E003, E012, 29, 99) point to maintenance tasks homeowners can handle: cleaning flame rods, verifying gas supply, descaling heat exchangers, and checking vents. Keep your owner's manual accessible, invest in a basic descaling kit (under $50 for a pump and solution), and clean the flame rod annually. These simple steps prevent the majority of error codes and extend your tankless heater's lifespan well past 15 years. If an error persists after basic troubleshooting or you encounter gas-related faults, call a licensed technician. A $150 service call now beats a $2,000 heat exchanger replacement later.