Takagi Water Heater Error Codes

Common Symptoms

• Error code displayed on Takagi front panel LED display
• Error code displayed on TM-RE20 remote controller
• Unit lockout — fires three times and shuts down (Error 11 or 12)
• Unit fires then shuts off — intermittent flame loss codes
• No hot water with no visible error code — check error history on TM-RE20
• Repeated same error code after power cycle reset — root cause not resolved

Most Likely Causes

1. 1

   Error 11 — No Ignition (Gas Supply, Ceramic Flame Rod, Igniter Electrode)

   Error 11 means the Takagi attempted ignition three times without establishing a flame and locked out. Diagnostic hierarchy: (1) Gas supply — confirm the shutoff valve is open (handle parallel to pipe). Test other gas appliances to confirm supply is active. Measure inlet gas pressure at the 1/8-inch NPT test port with a low-pressure manometer: natural gas 3.5–10.5 in. w.c.; LP 8–14 in. w.c. at static and dynamic (under firing load). A pressure drop greater than 1 in. w.c. under load indicates an undersized supply line or failing regulator. (2) Igniter electrode — inspect for cracks in the ceramic insulator; spark gap should be approximately 3–4 mm. (3) Ceramic-tipped flame rod — Takagi uses a ceramic-tipped flame rod. Clean the metal sensing tip with 0000 (four-aught) super-fine steel wool per Takagi service specifications. This is the most common Error 11 cause after the first year of operation. Do not use sandpaper on the ceramic-tipped rod. If cleaning doesn't clear the code after multiple attempts, the flame rod needs replacement.

2. 2

   Error 12 — Flame Loss During Operation

   Error 12 means the Takagi established a flame but it extinguished mid-cycle. Causes: (1) Dynamic gas pressure drop below 3.5 in. w.c. (NG) or 8 in. w.c. (LP) under full firing load — check with a manometer under firing conditions. (2) TK-200 modulating gas valve sticking or solenoid fault — the valve may hold a low-BTU flame but fail when commanded to modulate higher. Error 71 (gas valve solenoid) may appear alongside Error 12 on a failing TK-200 valve. (3) Vent obstruction — partial blockage of the exhaust flue or combustion air intake starves the flame at higher firing rates. Inspect both exterior vent terminals for debris, bird nests, ice, or spider webs. Power cycle to reset: press power off, wait 30 seconds, press on. Persistent Error 12 that returns immediately requires gas pressure testing and/or vent inspection before calling for parts.

3. 3

   Error 14 — Thermal Fuse Overheat Trip

   Error 14 means the thermal fuse inside the heat exchanger assembly has opened due to an overheat event. On Takagi condensing models, Error 14 almost always follows repeated unresolved Error 90 events — scale buildup creates localized hot spots that stress the thermal fuse until it trips open. The thermal fuse is a one-time safety device that cannot be reset — it must be replaced. Critical: always complete the full heat exchanger descale procedure (see Error 90 below) BEFORE replacing the thermal fuse. Installing a new fuse without descaling will result in the new fuse tripping again within the next few firing cycles. On Takagi non-condensing models, Error 14 more commonly indicates a blocked vent or exhaust gas recirculation into the combustion air intake rather than scale.

4. 4

   Error 16 — Outlet Water Temperature Overtemp (>185°F)

   Error 16 means the hot water outlet temperature sensor detected a temperature above 185°F — a safety shutdown to prevent scalding and damage. Causes: (1) Setpoint set too high via the TM-RE20 remote or the unit's front panel — confirm setpoint is 120°F for residential use (140°F maximum recommended by Takagi for anti-legionella applications). (2) Low flow rate causing the water to overheat — if flow drops below 0.5 GPM (T-KJr2) while the unit is firing at full BTU, outlet temperature can spike. Check for partially closed valves or severely clogged aerators. (3) Scale buildup restricting heat exchanger flow — see Error 90 for full descale procedure. (4) Defective outlet thermistor reading falsely high — test the outlet thermistor resistance with a multimeter and compare to the Takagi resistance-temperature chart in the service manual.

5. 5

   Error 32 — Cold Water Inlet Sensor Fault

   Error 32 indicates the cold water inlet temperature sensor (thermistor) has failed or is reading outside its expected resistance range. The inlet thermistor is used by the Takagi control board to calculate the required BTU output and confirm that water entering the heat exchanger is within a reasonable temperature range. A failed inlet thermistor can cause the unit to fire inefficiently, produce variable outlet temperatures, or lock out entirely. Diagnosis: shut off the cold water supply and unplug the unit. Locate the inlet thermistor on the cold water manifold (consult the service manual for your model). Test resistance with a multimeter — at room temperature (68°F), most Takagi thermistors read approximately 10 kΩ; consult the Takagi resistance-temperature chart for your model. If resistance reads open or shorted, replace with the OEM thermistor.

6. 6

   Error 33 — Heat Exchanger Outlet Sensor Fault

   Error 33 indicates a fault with the heat exchanger outlet temperature sensor. This sensor monitors the temperature of water exiting the primary heat exchanger to detect overheating and regulate combustion. A failed Error 33 sensor will cause the unit to fire erratically or shut down as a safety precaution. Diagnosis and replacement follow the same procedure as Error 32 — locate the thermistor at the heat exchanger outlet port, test resistance against the Takagi temperature-resistance chart, and replace if open or shorted.

7. 7

   Error 34 — DHW Outlet Sensor Fault

   Error 34 indicates a fault with the domestic hot water (DHW) outlet temperature sensor — the final temperature sensor before water exits the unit to the household. This thermistor is used for setpoint regulation and scalding protection. A drift in the DHW outlet sensor can produce water hotter or cooler than the setpoint without triggering a higher temperature error code, making Error 34 intermittent to diagnose. Test the sensor resistance at a known water temperature (use a calibrated thermometer at a nearby tap). Replace with the OEM Takagi DHW outlet thermistor.

8. 8

   Error 36 — Combustion Air Sensor Fault

   Error 36 indicates a fault with the combustion air temperature sensor, which monitors incoming combustion air temperature. Extreme ambient temperatures (very cold installation — below 32°F — or very hot utility room above 104°F) can push the sensor reading out of range. Confirm the installation environment is within Takagi's specified ambient temperature range (typically 32°F–104°F for residential models). If ambient temperature is within range and Error 36 persists, test the sensor resistance and replace if failed.

9. 9

   Error 37 — Exhaust Sensor Fault

   Error 37 indicates a fault with the exhaust temperature sensor. This sensor monitors flue exhaust temperature to detect vent blockages and abnormal combustion. A failed exhaust sensor can produce false Error 37 codes or fail to detect an actual vent blockage. Inspect the exhaust sensor probe — it is positioned in the flue path and can accumulate soot or debris on the probe tip, which affects readings. Clean the probe tip and retest before replacing the sensor assembly.

10. 10

    Error 38 — Primary Heat Exchanger Sensor Fault

    Error 38 indicates a fault with the primary heat exchanger temperature sensor. This sensor is mounted directly on or in the heat exchanger body to detect overheating from scale buildup. Scale deposits on the sensor probe itself can cause it to read falsely high, triggering Error 38 or Error 90 simultaneously. If both Error 38 and Error 90 appear together, perform the full heat exchanger descale procedure first — scale removal from the sensor probe may resolve both codes. If Error 38 persists after descaling, replace the sensor.

11. 11

    Error 52 — Modulating Gas Valve Fault

    Error 52 indicates a fault with the modulating gas valve — the Takagi TK-200 valve cannot be commanded to the requested modulation position. Causes: (1) Control signal wiring fault between the PCB and the TK-200 valve — inspect the wire harness for loose or corroded connectors. (2) TK-200 valve modulating actuator failure — the valve's proportional solenoid has failed and cannot modulate BTU output proportionally. Error 52 requires a licensed technician for gas valve replacement — this is not a DIY repair.

12. 12

    Error 61 — Fan Motor Fault

    Error 61 indicates the combustion fan motor has failed or is not achieving the commanded RPM. The fan is required for both forced combustion air supply and flue exhaust in Takagi's induced-draft design. Without correct fan operation, the unit cannot fire safely and shuts down. Causes: (1) Fan motor failure — the motor brushes or bearings have worn out. (2) Blocked vent causing excessive back-pressure that the fan cannot overcome — inspect exterior vent terminals for blockage before condemning the motor. (3) Fan control wiring fault — inspect the wire harness between the PCB and fan motor for loose connectors. Fan motor replacement requires a licensed HVAC/plumbing technician on gas appliances.

13. 13

    Error 65 — Flow Sensor Fault

    Error 65 indicates the flow sensor is not detecting water flow or is reading outside its expected range. Causes: (1) Flow sensor paddle debris — the turbine paddle inside the flow sensor can accumulate hard water mineral deposits or debris that prevent it from spinning freely. Shut off the cold water supply, remove the flow sensor, clear any debris from the paddle, and reinstall. (2) Flow sensor wiring fault — inspect the two-wire harness between the flow sensor and PCB for loose connectors. (3) Actual flow sensor failure — if clearing debris doesn't resolve Error 65, replace the flow sensor assembly. Note: Error 65 can also appear if the water flow rate is below the activation threshold (0.5 GPM T-KJr2) — confirm adequate flow before assuming sensor failure.

14. 14

    Error 71 — Gas Valve Solenoid Fault

    Error 71 indicates a fault with one of the gas valve solenoid coils — the TK-200 valve has both a main solenoid and a modulating actuator. A failed solenoid can prevent the valve from opening (no gas to burner = Error 11 or 12 alongside Error 71) or from modulating properly. Error 71 always requires a licensed gas technician — the TK-200 gas valve must be replaced as a complete assembly. Confirm wiring harness connections first before condemning the valve.

15. 15

    Error 90 — Combustion Abnormality (Scale Buildup — Full Descale Procedure)

    Error 90 is the most important Takagi fault code on condensing models in hard-water areas. It indicates combustion instability caused by calcium carbonate scale inside the primary heat exchanger. Scale acts as thermal insulation, creating localized hot spots that destabilize combustion — the control board detects abnormal heat exchanger or exhaust temperature swings and codes Error 90. In areas with water hardness above 120 ppm TDS, Error 90 typically appears within 2–3 years without annual descaling. Full descale procedure: (1) Shut off gas and electricity; close inlet/outlet isolation valves. (2) Connect a submersible pump to the cold service port with a return hose from the hot service port to a 5-gallon bucket. Use the Takagi flush kit or a compatible pump kit. (3) Fill the bucket with 3 gallons of undiluted white vinegar or CLR Calcium, Lime & Rust Remover. (4) Circulate for 60–90 minutes; replace with fresh vinegar if solution turns fully opaque early. (5) Flush with 5 gallons of clean water. (6) Restore operation and confirm Error 90 clears on the next firing cycle.

16. 16

    Error 99 — Overcurrent Fault

    Error 99 indicates an overcurrent condition detected by the Takagi control board — the electrical current draw from one or more internal components has exceeded the expected limit. Causes: (1) Fan motor drawing excessive current due to worn bearings or a developing failure. (2) Gas valve solenoid drawing excessive current due to a partially shorted solenoid coil. (3) Control board failure. Error 99 typically requires a service call — a technician can use an amp clamp on individual component circuits to identify which component is drawing excessive current. Do not continue operating the unit with an active Error 99 code as it indicates a potential electrical fault.

Quick DIY Checks

1. 1Step 1 — Read and record the error code from the front panel LED or TM-RE20 remote controller: the front panel displays the error number directly (11, 12, 14, etc.). On the TM-RE20 remote, press the error history button (refer to TM-RE20 manual — typically a wrench icon) to view stored fault codes with occurrence counts. Record the full error history — recurring codes (appearing multiple times per day) indicate a persistent root cause; single-occurrence codes may be transient faults that cleared on power cycle.
2. 2Step 2 — Reset procedure: most Takagi error codes can be cleared with a power cycle reset. To reset from the unit: press the power button to OFF, wait 30 seconds, press power button to ON. To reset from the TM-RE20 remote controller: refer to the TM-RE20 instruction manual — the remote reset sequence varies by firmware version but typically involves pressing and holding the power button for 5 seconds. If the error code returns within the first firing cycle after reset, the root cause is still active and must be diagnosed and repaired before the code will stay clear.
3. 3Step 3 — Error 11 (no ignition): confirm gas supply is active (shutoff valve open, other appliances work). Test inlet gas pressure at the 1/8-inch NPT test port with a low-pressure manometer (NG: 3.5–10.5 in. w.c.; LP: 8–14 in. w.c., both static and under firing load). If pressure is within spec, clean the ceramic-tipped flame rod with 0000 steel wool (see Takagi Water Heater Not Heating article for full procedure). Inspect the igniter electrode ceramic insulator for cracks. Power cycle to retest.

1. 4Step 4 — Error 12 (flame loss): after confirming gas pressure is within spec under firing load, inspect both exterior vent terminals for any blockage. For indoor installations, confirm the combustion air intake is not recirculating exhaust. If gas pressure and venting are confirmed clear, Error 12 that returns immediately after reset with no vent or gas pressure issues typically indicates the TK-200 gas valve is failing and requires a licensed technician.
2. 5Step 5 — Error 90 (combustion abnormality / scale): this is a maintenance error requiring the full descale procedure. Confirm Takagi isolator valve kits are installed (service port access). Perform the full vinegar or CLR circulation descale: 60–90 minutes circulation, then 5-gallon fresh water flush (detailed procedure in Takagi Water Heater Not Heating article). After descaling, power cycle and test. If Error 90 returns within the first few firing cycles after descaling, and if Error 14 (thermal fuse) also appears, the thermal fuse must be replaced — but always descale first.
3. 6Step 6 — Error 14 (thermal fuse): always complete the full Error 90 descale procedure first. After descaling, locate the thermal fuse on the heat exchanger assembly per the Takagi service manual for your model number (T-KJr2, T-H3, T-D2 positions differ). Replace with the OEM Takagi thermal fuse only — incorrect temperature-rated aftermarket fuses risk premature re-trip. Power cycle and test for Error 14 clearance.
4. 7Step 7 — Errors 32–38 (sensor faults): locate the identified sensor on the Takagi unit (consult the service manual parts diagram for your model number). Shut off cold water supply and unplug the unit. Test sensor resistance with a multimeter and compare to the Takagi resistance-temperature curve in the service manual (most Takagi thermistors read approximately 10 kΩ at 68°F). A reading of zero (shorted) or infinite (open) confirms sensor failure — replace with the OEM Takagi thermistor for your model.
5. 8Step 8 — Error 65 (flow sensor): shut off the cold water supply. Remove the flow sensor from the cold water inlet manifold. Inspect the turbine paddle inside the sensor housing for mineral deposits or debris. Clear any debris from the paddle and reinsert the turbine into the housing — it should spin freely by hand. Reinstall the sensor, restore water supply, and power cycle. If Error 65 returns, replace the flow sensor. Also confirm that flow at the fixture is above the minimum activation threshold (0.5 GPM for T-KJr2; 0.26 GPM for T-D2).
6. 9Step 9 — Errors 52, 61, 71, 99 (gas valve, fan motor, solenoid, overcurrent): these codes indicate faults in gas-handling or electrical drive components that require a licensed HVAC/plumbing technician. Before calling: (1) Check that all wire harness connectors to the relevant component are fully seated — loose connectors can produce transient component fault codes. (2) Inspect the exterior vent terminals for blockage (for Error 61 fan motor fault — excessive back-pressure can overload the fan). Power cycle and retest. If the code returns immediately, schedule a service call.

Repair vs Replace

Recommended Tools & Parts

• Takagi Ceramic Flame Rod / Flame Sensor Assembly

  OEM ceramic-tipped flame rod for Error 11 that persists after 0000 steel wool cleaning. Match to your exact Takagi model number (T-KJr2, T-H3, or T-D2 variants differ).

  $20–$50

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• Takagi Thermal Fuse Assembly

  OEM one-time thermal fuse for Error 14. Always complete the full heat exchanger descale for Error 90 before installing — a new fuse will re-trip immediately if scale is not removed first.

  $25–$65

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• Takagi Flow Sensor Assembly

  Replacement flow sensor for Error 65. Includes turbine paddle assembly and O-ring. Match to your model — T-KJr2, T-H3, and T-D2 use different flow sensor specs.

  $30–$70

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• Takagi Inlet / Outlet Thermistor (Sensor Set)

  OEM thermistor sensors for Error 32 (inlet), 33 (HX outlet), 34 (DHW outlet), 36 (combustion air), 37 (exhaust), or 38 (primary HX sensor). Confirm the correct sensor position and part number from the Takagi service manual for your model.

  $15–$45 each

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• Takagi Flush Kit (Descale Kit)

  Takagi-branded descaling flush kit for the Error 90 heat exchanger descale procedure. Includes submersible pump, hoses, and service port fittings sized for Takagi isolator valve kits.

  $40–$70

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

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