Takagi tankless water heater code 101
Abnormal combustion (warning). Code 101 means the same thing on all 2 Takagi series documented here — but the fix, and what it costs, is still worth reading for your exact unit.
What code 101 means on each Takagi series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Condensing | Abnormal combustion (warning) | Call a pro | $150–$900 |
| Non-Condensing | Abnormal combustion (warning) | Call a pro | $150–$900 |
Each row opens the full page for that generation. We hold manuals for Condensing and Non-Condensing, and each one gets its own reading of code 101 — what Takagi documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 2 series in four columns, which is enough to route you and not enough to explain anything. This is the Takagi wording behind each row, one entry per manual, so you can see where the 2 readings of code 101 agree and where they part company.
Condensing — Abnormal combustion (warning)
The warning that precedes error 991. Takagi's own checks for it start with blockage in the airway — vent obstructions such as birds' nests or trash, a backflow preventer installed backwards, the heat exchanger, the fan — then manifold pressure, then contaminated intake air from dust, lint, or kitchen grease, then weather and altitude settings.
Non-Condensing — Abnormal combustion (warning)
The warning that precedes error 991 — the unit is telling you combustion is not right while still running. Shown as 10 on a T-K4 or T-KJr2 remote, or five flashes of the red LED.
Does it matter which Takagi you have?
Condensing and Non-Condensing all route code 101 the same way: a professional, at $150–$900. That makes it one of the Takagi numbers you can act on before working out which unit you own.
What to check first, whatever your series
These checks are on the manufacturer's list for every Takagi series that reports code 101, so they are safe to work through before you have identified your exact unit. They also cost nothing.
- Check that your carbon monoxide alarms work.
- Book a licensed professional.
That is 2 of the 4 checks documented for code 101. The rest differ by generation, so if none of those explains it, go to your own series above.
Which Takagi do you have?
On the 2 series that report code 101, the model number on the rating label starts T — match yours against the 3 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Takagi Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 14), read Aug 2026 — the manufacturer's own documentation for this Takagi range.
Source: Takagi Non-Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 12), read Aug 2026 — the manufacturer's own documentation for this Takagi range.
Parts, guides and symptoms behind code 101
Code 101 on these 2 Takagi series points at 2 parts and 2 symptoms, each named by the manufacturer's own procedure for this code.