Takagi Error Code 111: Ignition Failure (Heater Won't Light)
What the code means
Takagi's service handbook for its condensing models (240, 340 and 540) defines code 111 as the water heater not firing after three failed ignition attempts. Code 121 is the related flame loss code, where the heater had a flame during a heating cycle, lost the flame signal, and couldn't relight after three tries. Takagi notes both codes reset on their own when water flow through the heater stops or power is interrupted, so the code may clear and come back on the next hot-water draw if the cause isn't fixed. On the non-condensing 510 (T-D2) and 910 (T-M50) the display shows 111 for the same ignition failure; the older 110 (T-KJr2) and 310 (T-K4) show it as three flashes or code 11 instead.
Likely causes
- No gas or not enough gas: a closed valve, an empty propane tank, air or debris in the gas line, or an undersized gas line
- A faulty pressure regulator at the gas meter, or a cold propane regulator during cold parts of the day
- Gas pressure dropping too far while the heater runs (Takagi flags a drop of more than 1 to 1.5 inches of water column under full demand on condensing models)
- A tripped high limit switch, often from scale in the heat exchanger or very hot incoming water such as from a solar preheat system
- A blown overheat cutoff fuse (OHCF)
- A blocked vent, burner or heat exchanger (bird nests, animals, trash)
- A disconnected clear plastic tube between the proportional gas valve and the combustion chamber
- A dirty or damaged flame sensor (flame lights for only 1 to 2 seconds, then goes out)
- A weak or missing igniter spark, from loose igniter wires or a failed igniter
- A failed main gas valve, gas solenoid valve or computer board
Safe DIY checks
Unplug the appliance (or switch off its breaker) and shut off the water supply valves before removing panels or disconnecting hoses. Keep towels handy for residual water.
- Turn the power to the heater off and back on, then open a hot tap. Takagi says code 111 resets when power is interrupted or water flow stops, so note whether it lights or the code comes right back.
- Make sure the gas supply valve to the heater is fully open and, on propane, that the tank isn't empty. If other gas appliances also aren't working, the problem is the gas supply, not the heater. If you smell gas, leave and call your gas company.
- Check the outdoor vent and air intake terminations for bird nests, leaves, trash, snow or ice.
- Reset the high limit switch: with the power off and the front cover removed, push in the button in the middle of the switch until you hear and feel it click, then power back on and test. If it trips again, Takagi says the heater may need descaling, and that very hot incoming water (for example from a solar system) can also cause it.
- Look through the sight glass next to the igniter while the heater tries to light. Takagi says a strong blue spark stays steady and in place, while a weak spark jumps around. Note what you see for the technician.
- If the flame comes on for only 1 to 2 seconds before going out, the flame sensor likely needs cleaning; Takagi's handbook covers cleaning the rod assembly, and it's a job a technician can do quickly if you're not comfortable opening the unit.
🛠 When to call a pro
- Have a technician measure the inlet gas pressure in standby and with every hot tap open, and check the gas line size and the meter or propane regulator. Takagi lists natural gas inlet pressure at 4 to 10.5 inches W.C. and propane at 8 to 14 inches W.C. on its condensing models.
- Have the overheat cutoff fuse (OHCF) checked for continuity if the high limit switch is fine but you don't hear the gas valves click on.
- Have the igniter wiring, igniter rod and igniter voltage checked, and the igniter replaced if there's no spark or a weak one.
- Have the main gas valve and gas solenoid valves resistance-tested and replaced if out of range, and the computer board replaced if the igniter voltage is wrong.
- Call for a descale if the high limit switch keeps tripping. Takagi's Technical Service Department can also help with code 111 that won't clear.
Parts that commonly fix it
Always match the part number to your exact model.
Gas leak detector
Useful when checking gas supply problems; leave the house and call the gas company if you smell gas.
Search eBay →Sources
- Takagi On-Demand Water Heater Service Handbook for 240, 340 & 540 Condensing Models (2000534342): Code 111 or 121, three failed ignition attempts vs lost flame signal, internal or external cause such as no gas, auto-reset when water flow stops or power is interrupted, gas pressure drop of more than 1 to 1.5 in. W.C., cold propane regulator, high limit switch reset and descaling, solar preheat, OHCF, vent blockage, air tube, spark check through sight glass, igniter voltage, flame sensor cleaning, MV and SV resistance; inlet pressure 4 to 10.5 in. W.C. natural gas and 8 to 14 in. W.C. propane
- Takagi Troubleshooting Guide 321923-000 for 110 (T-KJr2), 310 (T-K4) and 510 (T-D2): Error Code 111 (510) or three flashes / 11 (110, 310), ignition failure after three attempts, hi-limit reset, gas supply and regulator, OHCF, flame sensor, igniter spark, vent blockages, PC board or gas solenoid fault
- Takagi Troubleshooting Guide 321925-000 for 910 (T-M50): Error Code 111, ignition failure, same checklist
Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.