Takagi Non-Condensing Code 510
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.
Also displayed as: 51
Call a proThe verdict
Call a licensed plumber
Gas train work with no owner-level step. The valve assembly is the expensive outcome; wiring or a connector is the cheap one, and only a technician can separate them.
Typical cost: $250–$1,100
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.
- 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.
Frequently asked questions
There is no 551 on my unit.
Not on this range. The condensing models have a separate 551 for the solenoid valves; here the T-KJr2 and T-K4 have a two-digit 55 with no three-digit equivalent, and 510 covers the gas valves generally.
Code 510 on other Takagi series
The same code number can mean something different on another series — make sure you're reading the page for your exact unit:
Don't confuse this with
2 other Takagi Non-Condensing codes point at a valve too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: