Takagi tankless water heater code 510
Your series decides which reading applies. Across the 2 Takagi series documented here, code 510 is listed as main and solenoid gas valve fault (1 series) and abnormal gas valves (1 series). Find your series in the table below, where those readings route to a professional.
What code 510 means on each Takagi series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Condensing | Main and solenoid gas valve fault | Call a pro | $250–$1,100 |
| Non-Condensing | Abnormal gas valves | Call a pro | $250–$1,100 |
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 510 — 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 510 agree and where they part company.
Condensing — Main and solenoid gas valve fault
The main gas valve and its solenoid are not behaving as the board expects. This is the gas train — the assembly that decides whether and how much gas reaches the burner.
Non-Condensing — Abnormal gas valves
The gas valves are not behaving as the board expects. Note the wording here: on the non-condensing range Takagi calls this "abnormal gas valves" as one code, where the condensing range splits main-and-solenoid (510) from the solenoid valves themselves (551). Shown as 51 on a T-K4 or T-KJr2 remote, or six flashes of the red LED.
Does it matter which Takagi you have?
Condensing and Non-Condensing all route code 510 the same way: a professional, at $250–$1,100. 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 510, so they are safe to work through before you have identified your exact unit. They also cost nothing.
- Turn the heater off and close the manual gas valve below it.
- If you smell gas, leave the building and call your gas utility from outside.
- Book a licensed professional.
That is 3 of the 3 checks documented for code 510. 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 510, 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 510
Code 510 on these 2 Takagi series points at 1 part and 1 symptom, each named by the manufacturer's own procedure for this code.