Takagi Tankless Error Codes: What They Mean & What to Do
Your Takagi is showing a three-digit code. Here’s what each one means and what to do next.
Updated October 2026 · By the Hot Water Heater Factory team
Takagi error codes and what they mean
| Code | What it means | What to do |
|---|---|---|
| 031 | Incorrect DIP switch settings | A technician needs to check this. Text us the code. |
| 101 | Warning related to code 991 (gas type and venting) | Check the outside vent for blockages, then text us. |
| 111 | Ignition failure | Make sure the gas is on (and the propane tank isn’t empty), then text us. |
| 121 | Loss of flame | Often low gas supply or venting. Text us the code. |
| 311, 321, 331 | Temperature sensor (thermistor) shorted or disconnected | A technician needs to check this. Text us the code. |
| 391 | Air-fuel ratio rod failure | A technician needs to check this. Text us the code. |
| 441 | Flow sensor failure | A technician needs to check this. Text us the code. |
| 510, 551 | Gas valve solenoid problem | A technician needs to check this. Text us the code. |
| 611 | Fan motor fault | A technician needs to check this. Text us the code. |
| 651 | Flow adjustment valve fault | A technician needs to check this. Text us the code. |
| 661 | Bypass valve fault | A technician needs to check this. Text us the code. |
| 701 | Computer board fault | A technician needs to check this. Text us the code. |
| 711 | Gas valve solenoid drive circuit failure | A technician needs to check this. Text us the code. |
| 721 | False flame detection | A technician needs to check this. Text us the code. |
| 741 | Communication error with the remote controller | Check the remote’s connection. If it continues, text us. |
| 991 | Imperfect combustion | Turn the unit off. Often a gas or venting problem. A technician needs to check this. Text us the code. |
Code meanings come from Takagi’s installation manuals. Codes can vary by model, so check your owner’s manual too.
What should I do when my Takagi shows a code?
- Write down the code. If it shows more than one, note each one.
- Turn off the hot water taps. Some codes clear when the unit is turned off and back on, but if the code comes back, the unit is telling you something.
- Don’t keep resetting codes for overheating, flame or gas problems.
- Text us the code and a photo of the label. We’ll tell you what it likely means and bring the right parts.
Other brands: Rinnai codes · Navien codes · Noritz codes. Many codes come from scale buildup; see tankless descaling and maintenance.
Questions we hear a lot
What does 111 mean on a Takagi?
Ignition failure. The unit didn’t light. Check that the gas is on and the propane tank isn’t empty, then text us.
What does 991 mean on a Takagi?
Imperfect combustion, often from a gas supply or venting problem. Turn the unit off and have it checked.
What does 101 mean on a Takagi?
It’s a warning related to code 991, pointing to a gas type or venting issue. Check the outside vent and text us before it turns into a shutdown.
Takagi showing a code? Text us now.
Send a photo of your water heater’s label and tell us what’s happening. A real person texts you back.