Tankless Water Heater Error Codes — Rinnai, Navien, Rheem, Noritz Guide

Common Symptoms

• Error code on the display — unit in lockout, not producing hot water
• Rinnai shows error 10, 11, 12, 16, 25, 52, 61, or 65
• Navien shows E003, E004, E010, E012, E016, E030, or E439
• Rheem shows error code 11, 13, 76, C7, or service code 29
• Noritz shows error code 10, 11, 12, 14, 16, 70, or 90
• Takagi shows C4, C7, C8, or 111 on the display
• Bosch shows E9, EA, EE, or numeric fault on the display

Most Likely Causes

1. 1

   Ignition Failure Codes — Rinnai 11, Navien E003, Rheem 11, Noritz 11, Takagi C4

   Ignition failure codes (all variants of '11' or 'E003' / 'C4') mean the unit attempted ignition but the burner did not light within the startup window. Root causes are identical across all brands: insufficient gas supply pressure, flow below the minimum activation threshold (clogged inlet screen), venting blockage causing flue gas recirculation into the combustion air intake, or an oxidized flame sensor rod that cannot confirm ignition. Diagnostic order is the same for all brands: (1) verify gas supply is on and other gas appliances work, (2) clean inlet filter screen, (3) inspect vent termination caps, (4) clean flame sensor rod with fine emery cloth. Reset the unit after each step and test with a full-flow hot draw.

2. 2

   Flame Loss During Operation — Rinnai 12, Navien E012, Rheem 13, Noritz 12

   Flame loss codes (Rinnai 12, Navien E012, Rheem 13, Noritz 12) indicate the burner ignited successfully but the flame went out mid-cycle. This is distinct from an ignition failure. Causes: gas pressure drop during high demand (especially on LP systems with a nearly empty or undersized regulator), partial venting blockage that allows initial ignition but starves the burner of combustion air at higher BTU output, or a failing modulating gas valve that cannot sustain gas flow under load. Condensation in PVC exhaust vent runs (common on Navien condensing models in winter) causes partial blockage that triggers this code. Inspect vent runs for sagging joints that trap condensate.

3. 3

   Exhaust / Venting Error — Rinnai 16, Navien E030, Rheem 76, Noritz 16

   Venting error codes (Rinnai 16 = exhaust blockage, Navien E030 = overheat or exhaust blockage, Rheem 76 = exhaust thermistor fault, Noritz 16 = exhaust blocked) all point to the vent system. Rinnai 16 indicates the exhaust temperature sensor detected abnormally high exhaust temperature — caused by a blocked exhaust pipe or recirculation of hot flue gases back into the unit. Navien E030 triggers when the unit overheats due to reduced combustion airflow or blocked exhaust. Rheem error 76 is specifically an exhaust thermistor failure (not always a blockage). Noritz 16 is a direct exhaust blockage detection. For all: inspect exterior vent termination first, then trace the interior vent run for disconnected joints, sagging, or condensate pooling.

4. 4

   Outlet Thermistor Fault — Navien E010, Noritz Error 32, Rinnai Error 32

   E010 on Navien, Error 32 on Rinnai, and Error 32 on Noritz all indicate a fault on the outlet (hot water) thermistor — the NTC temperature sensor that monitors outgoing water temperature. A failed thermistor either reads open circuit (OL on multimeter) or severely out of range. At room temperature (77°F), a healthy 10kΩ NTC thermistor reads approximately 10kΩ. An OL or near-zero reading indicates failure. Thermistor replacement is straightforward: disconnect power, open the cover, locate the thermistor connector (labeled TH-O or 'outlet'), disconnect and test, replace if out of range. Thermistors for all brands are available online for $15–$40.

5. 5

   Rinnai Error 10 — Abnormal Combustion / Dirty Burner

   Rinnai Error 10 indicates abnormal combustion — the control board detected an irregular flame pattern through the ionization sensor. Most common cause: a dirty or partially blocked burner from dust accumulation, spider webs in the combustion chamber, or a partially clogged gas orifice. This code also appears when the gas-to-air mixture is off due to a partially blocked combustion air intake. Resolution: with gas and power off, remove the burner assembly cover and inspect the burner for visible contamination. A compressed air blow-out of the combustion chamber clears most debris. If the code persists after cleaning, the gas valve modulation trim may need professional recalibration.

6. 6

   Navien E439 — Condensate Neutralizer Blocked

   E439 is specific to Navien NPE condensing models. It indicates the condensate neutralizer cartridge is exhausted or the condensate drain line is blocked. Navien condensing units produce 1–3 gallons of acidic condensate per day (pH approximately 3.5) that must be neutralized (magnesium oxide pellets raise it to pH 6.5–7.0) before draining. When the neutralizer pellets exhaust and pack together, condensate cannot flow through and backs up, triggering E439. Resolution: replace the condensate neutralizer cartridge (Navien part: CSG-N0003E or CSG-B0053E, depending on model). Also flush the drain line with water to clear algae growth. Navien recommends annual neutralizer replacement.

7. 7

   Rheem Error Code 11 / 13 — Ignition Failure and Flame Sensor

   Rheem RTGH and RTEX series use numerical codes: Error 11 = no ignition (identical in cause to Rinnai 11 — gas supply, inlet flow, vent blockage, flame sensor). Error 13 = burner flame loss — identical in cause to Rinnai 12. For Rheem Error 11: use the same diagnostic sequence: verify gas supply, clean inlet filter screen, inspect vent termination, clean flame sensor rod. For Rheem Error 13: check gas pressure during full demand (use a manometer at the test port on the gas valve — should read minimum 3.5 inches WC for natural gas under full flow). A pressure drop below 3.5 inches WC under load indicates an undersized supply line or failing regulator.

Quick DIY Checks

1. 1Step 1 — Record the exact error code before any reset: note the alphanumeric code displayed (e.g., '11', 'E003', '76'). On Rinnai units: the code is displayed as a number on the MC-91-2 or PC-B remote controller. On Navien units: the E-code appears on the integrated LCD display and on the NaviLink app if connected. On Rheem: the code shows on the digital display on the unit face. On Noritz: the code appears on the ERC-310 remote controller display. On Takagi: the code appears on the TM-RE30 remote controller. On Bosch: the code appears on the digital display. After recording, proceed with the specific diagnosis steps below before pressing reset — resetting clears the display but the fault history is stored in the unit's memory and accessible via service mode.
2. 2Step 2 — Rinnai error code diagnosis and reset procedure: RINNAI ERROR 10 (Abnormal Combustion): check combustion air intake for blockage; inspect burner for debris; confirm gas supply pressure; call a tech if code persists after cleaning. RINNAI ERROR 11 (No Ignition): verify gas valve is open; clean inlet filter screen; inspect vent termination; clean flame sensor rod with emery cloth. RINNAI ERROR 12 (Flame Failure): check for partial vent blockage (exhaust pipe sagging); test gas pressure under full load; inspect for condensate in vent runs. RINNAI ERROR 16 (Exhaust Blocked): inspect exterior exhaust termination cap for nest or ice; trace interior vent run for disconnected joints. Reset Rinnai: press the On/Off button on the controller to clear the code. Persistent codes after multiple resets indicate an unresolved hardware fault.
3. 3Step 3 — Navien error code diagnosis and reset procedure: NAVIEN E003 (Ignition Failure): same as Rinnai 11 — gas supply, inlet screen, vent, flame sensor. NAVIEN E010 (Outlet Thermistor Fault): test the outlet thermistor with a multimeter — should read ~10kΩ at 77°F; replace if OL or out of range. NAVIEN E012 (Flame Failure): check for condensate pooling in vent run sagging joints; verify gas pressure under load. NAVIEN E030 (Exhaust Blockage / Overheat): inspect exterior vent termination; on Navien NPE condensing models, check for condensate freeze at termination in winter. NAVIEN E439 (Condensate Neutralizer): replace neutralizer cartridge (annual maintenance item on all NPE models). Reset Navien: press the Reset button on the front panel or the NaviLink remote. Multiple E003 or E012 events within 24 hours require hardware investigation — do not repeatedly reset without addressing the root cause.

1. 4Step 4 — Rheem error code diagnosis and reset procedure: RHEEM ERROR 11 (No Ignition): gas supply check, inlet filter cleaning, vent inspection, flame sensor cleaning — identical sequence to Rinnai 11. RHEEM ERROR 13 (Flame Loss): gas pressure test under full demand; vent blockage inspection; check gas valve operation. RHEEM ERROR 76 (Exhaust Thermistor Fault): test the exhaust thermistor with a multimeter — an open-circuit thermistor at the exhaust vent causes Error 76. Thermistor replacement is required. RHEEM SERVICE CODE 29 (Flow Sensor): clean or replace the flow sensor turbine assembly. Reset Rheem RTGH units: press the Reset button on the face of the unit. For Rheem RTEX electric tankless: turn off the circuit breaker for 30 seconds and restore — there is no manual reset button on RTEX units.
2. 5Step 5 — Noritz, Takagi, and Bosch error code diagnosis: NORITZ ERROR 10 (Abnormal Combustion): same as Rinnai Error 10 — combustion air quality and gas-air mixture. NORITZ ERROR 11 (Ignition Failure): same diagnosis as Rinnai 11. NORITZ ERROR 12 (Flame Failure): same as Rinnai 12. NORITZ ERROR 14 (Flow Sensor): clean or replace the flow sensor assembly. NORITZ ERROR 16 (Exhaust Blocked): inspect exhaust vent termination and interior run. Reset Noritz: press and hold the Reset button for 3 seconds. TAKAGI C4 (Ignition Failure): gas supply, inlet screen, vent, flame sensor — same as Rinnai 11. TAKAGI C7 (Water Temperature Abnormal): check outlet thermistor; descale heat exchanger. TAKAGI C8 (Abnormal Combustion): combustion chamber inspection required. Reset Takagi: remove power at the breaker for 30 seconds. BOSCH ERROR E9 (Ignition Failure): gas supply, vent, inlet filter, flame sensor. BOSCH ERROR EA (Temperature Fault): thermistor diagnosis. BOSCH ERROR EE (Fan Fault): fan motor inspection. Reset Bosch Therm units: hold the Reset button for 5 seconds.
3. 6Step 6 — Access error code history via service mode: most modern tankless units log a history of recent error codes that persists after reset — useful when you arrive after the unit has already been reset. RINNAI: hold the Mode button + Up arrow on the RC-91 controller for 3 seconds to enter service mode; navigate to 'Error History'. NAVIEN: from the main menu, navigate to Service → History → Error Log; shows the last 5 error codes with timestamps. NORITZ: hold the Reset button and power button simultaneously for 5 seconds on the ERC-310 controller to enter history mode. RHEEM RTGH: press and hold the Mode button for 5 seconds to access the error log on the display. TAKAGI: hold the Reset button and the Display button simultaneously for 5 seconds on the TM-RE30 controller. Error history often reveals recurring codes (indicating a chronic issue) vs. one-time faults (power surge, momentary gas pressure drop).
4. 7Step 7 — When to call a professional technician: some error codes reliably indicate components that require certified technician service: (1) Any gas valve fault code (Rinnai 52, 71-73; Navien E047; Noritz 65): gas valve solenoid or modulation circuit failure. (2) PCB fault codes (Rinnai 70; Navien E109/E110): control board failure after ruling out wiring and fuses. (3) Heat exchanger overtemp codes (Navien E016; Noritz 70): potential heat exchanger damage from scale neglect or freeze damage. (4) Recurring ignition failures (same code returning within 24 hours after proper reset): systematic fault requiring hands-on diagnosis. (5) Combustion analysis codes (Rinnai 10; Takagi C8): gas-air mixture calibration requires combustion analyzer equipment. For warranty units: always contact the manufacturer's technical support line with the serial number before authorizing third-party service — warranty repair by authorized service avoids out-of-pocket cost.

Repair vs Replace

Recommended Tools & Parts

• Navien Condensate Neutralizer Cartridge (CSG-N0003E / CSG-B0053E)

  Replacement condensate neutralizer cartridge for Navien NPE condensing tankless units. Resolves E439 error. Replace annually in hard water areas, every 2 years otherwise. Two cartridge SKUs — confirm your NPE model before ordering.

  $20–$50

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• Rinnai Flame Sensor Rod (Universal Tankless Replacement)

  Replacement ionization flame sensor rod for Rinnai tankless units. Resolves persistent Error 11 and Error 12 after cleaning fails to restore proper ionization current. Order by model number for correct mounting bracket.

  $15–$40

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• NTC 10kΩ Outlet Thermistor — Navien / Rinnai / Noritz

  Outlet water temperature thermistor (NTC 10kΩ) for tankless water heaters. Resolves Navien E010, Rinnai Error 32, Noritz Error 32. Order brand and model-specific for correct connector type.

  $15–$40

  Buy on Amazon →

• Rheem RTGH Exhaust Thermistor Assembly

  Replacement exhaust thermistor for Rheem RTGH tankless units. Resolves Rheem Error 76 (exhaust thermistor fault). Confirm your RTGH model suffix (e-84DVLN, e-95DVLN, etc.) for the correct part.

  $20–$50

  Buy on Amazon →

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

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