HeatingCodesTakagi tankless error codes 11 and 12: ignition failure and flame loss
What error 11 and 12 mean
Takagi's troubleshooting guide (321923-000) defines error 11 (111 on the T-D2) as ignition failure: the heater does not fire after three failed attempts at ignition. Error 12 (121 on the T-D2) is flame loss: the flames disappear while the unit is still supposed to be operating. On the T-KJr2 and T-K4, the red LED flashes three times for both of these, so you need the remote controller code to tell them apart.
Takagi's checklist, in plain language
| Item | What the guide says |
|---|---|
| Hi-limit switch | Verify it is not tripped. If the unit fires after it is reset, the cause of the trip must be determined; Takagi asks that its technical service department be contacted. |
| Gas supply | Verify enough gas reaches the heater and the line is clear of debris or air. A faulty pressure regulator at the meter is possible. For propane units, colder periods of the day result in a cold regulator and may cause this problem. |
| Gas supply pressure | Should be within specification both in standby and while the heater is running. |
| Clear plastic tube | The tube between the proportional gas valve and the combustion chamber must be attached. |
| Overheat cutoff fuse | May have been compromised. If so, contact Takagi technical service. |
| Flame sensor | If the flame lights for only 1 to 2 seconds before going out, clean the flame sensor. |
| Igniter (error 11) | Check for spark through the sight glass. A strong blue spark stays steady; a weak spark jumps around. Weak or no spark means check wire connections, then replace the igniter. |
| Venting | Check for blockages such as bird nests, animals or trash. |
| Board or gas solenoid | A PC board fault or a gas solenoid fault. Contact Takagi technical service. |
The propane note matters in winter: Takagi says a cold regulator on a propane unit can cause these errors during colder parts of the day. If you have propane and the heater fails on cold mornings and works later, tell your technician.
What is safe and what is not
The guide is written for installers. Resetting the hi-limit, measuring gas pressure, checking the fuse and cleaning the flame sensor involve opening a gas appliance. A homeowner can check that gas is on, make sure the outdoor vent is not blocked by snow or ice, and note the exact code.
Safe homeowner checks for Takagi tankless error 11 or 12
- Check that gas is onSee whether another gas appliance works. If you have propane, check that the tank is not empty. If you smell gas, leave and call your gas utility from outside.
- Check the outdoor ventFrom the ground, clear snow, ice or debris from the heater vent termination. Do not remove the vent.
- Turn a hot tap fully on and try againThe heater fires when water flow is high enough. Open one hot tap fully. If the code returns, stop.
- Call a technicianIf error 11 or 12 returns, call a qualified technician or the Takagi technical service line given in your manual.
Frequently asked questions
How do I tell error 11 from error 12 on the LED?
You cannot from the LED alone: Takagi lists three flashes for both. The remote controller shows the two-digit code. On the T-D2 the display shows 111 or 121.
Can a dirty flame sensor cause error 12?
Takagi lists cleaning the flame sensor when the flame comes on for 1 to 2 seconds and then goes out. It is one of several possible causes.
Does this apply to condensing Takagi models?
The guide covers the non-condensing T-KJr2, T-K4 and T-D2. Condensing models have their own documents.
Sources
- Troubleshooting Guide 321923-000 (9/12/11): Non-Condensing On-Demand Water Heaters, T-KJr2, T-K4 and T-D2 (110, 310 and 510 models) (Takagi (A.O. Smith Water Products Company)) Covers: Takagi T-KJr2, T-K4 and T-D2 non-condensing tankless water heaters, indoor and outdoor. Other Takagi models have their own guides.
Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.