Takagi tankless water heater code 651
Your series decides which reading applies. Across the 2 Takagi series documented here, code 651 is listed as flow adjustment valve fault (1 series) and flow adjustment valve fault (easy-link systems) (1 series). Find your series in the table below, where those readings route to a replacement part.
What code 651 means on each Takagi series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Condensing | Flow adjustment valve fault | Part replacement | $200–$600 |
| Non-Condensing | Flow adjustment valve fault (Easy-Link systems) | Part replacement | $200–$600 |
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 651 — 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 651 agree and where they part company.
Condensing — Flow adjustment valve fault
The flow adjustment valve, which meters how much water passes through the unit, is not behaving. It is one of the two ways the heater controls outlet temperature, the other being how hard it fires.
Non-Condensing — Flow adjustment valve fault (Easy-Link systems)
The flow adjustment valve, which meters how much water passes through the unit, is not behaving. Takagi marks this code Easy-Link system only on the non-condensing range.
Does it matter which Takagi you have?
Condensing and Non-Condensing all route code 651 the same way: a replacement part, at $200–$600. 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 651, so they are safe to work through before you have identified your exact unit. They also cost nothing.
- Note whether the temperature swings and at what flow rates.
- Book a service call.
That is 2 of the 2 checks documented for code 651. 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 651, 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. 13), 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 651
Code 651 on these 2 Takagi series points at 1 part and 1 symptom, each named by the manufacturer's own procedure for this code.