Takagi Non-Condensing Code 121
Flame loss. The flame disappeared while the unit was still supposed to be running. Shown as 12 on a T-K4 or T-KJr2 remote, or three flashes of the red LED — the same count as ignition failure.
Also displayed as: 12
Call a proThe verdict
Call a licensed plumber
One occurrence after a gas interruption can be nothing. A repeating one means the flame is genuinely going out or not being seen, and that needs gas pressure measured under load.
Typical cost: $150–$900
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Non-Condensing — not averaged across the brand.
Source: Takagi Non-Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 12), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- If you smell gas, leave and call your gas utility from outside.
- Confirm gas is on and other gas appliances work.
- Note whether it happens when another gas appliance fires.
- Book a licensed professional if it repeats.
Frequently asked questions
How is this different from 111?
111 is failing to light. 121 is losing the flame after it was established. They share most of their causes, which is why Takagi gives them the same red LED flash count.
Code 121 on other Takagi series
Other Takagi series report code 121 under the same fault name, but each manual is transcribed separately and they do not read alike:
Don't confuse this with
One other Takagi Non-Condensing code points at flame detection too. They are the same symptom reported from a different place in the unit, so which one the display shows is what tells you where to look: