Takagi Error Code 121: Flame Failure
Warning: The Takagi tankless water heater has detected a flame failure. This could indicate a gas leak or carbon monoxide risk. Shut down the unit immediately and call a qualified technician.
How to Fix Takagi Code 121
- Step 1: Ensure that the gas supply to the unit is turned on. Check the gas shut-off valve near the unit and at the gas meter.
- Step 2: Check for any obstructions around the vent termination outside the house. Clear any snow, ice, or debris.
- Step 3: Reset the unit by turning it off and then on again. If the error persists, do not continue to reset it. Call a qualified HVAC technician or plumber immediately.
How to Reset Takagi Code 121
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
What does 121 mean?
Error code 121 on your Takagi tankless water heater indicates that the unit attempted to ignite the burner, but the flame was not properly established or was lost during operation. This is a safety feature that shuts down the unit to prevent unburnt gas from accumulating, which could lead to a dangerous situation. The system monitors the flame through a flame rod sensor. If the sensor doesn't detect a flame when it should, or if the flame is lost mid-cycle, it triggers this error. This issue prevents the unit from providing hot water and needs immediate attention.
Affected Models
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Flame Rod Sensor | — | — |
| Gas Valve | — | — |
| Igniter | — | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| 101 | Combustion Abnormality | Critical |
| 111 | Ignition Failure | Critical |
| 200 | Overheating | Warning |
| 207 | Bypass Valve Error | Warning |
| 291 | Flow Rate Issue | Warning |
| 312 | Outlet Temp Sensor | Warning |
| 321 | Inlet Temp Sensor | Warning |
| 391 | Exhaust Temp Sensor | Warning |
| 510 | Gas Solenoid Valve | Critical |
| 610 | Fan Motor Fault | Warning |