Takagi Condensing Code 510
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.
Call a proThe verdict
Call a licensed plumber
Gas train work with no owner-level step. The gas valve assembly is the expensive outcome; wiring or a connector at the same solenoid 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 Condensing — not averaged across the brand.
Source: Takagi Condensing Models On-Demand Water Heater Troubleshooting Guide (p. 13), 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
How is 510 different from 551?
Takagi lists 510 as the main and solenoid gas valve, and 551 as the solenoid valves specifically. Both are the gas train; 551 narrows it to the solenoids.
Code 510 on other Takagi series
Code 510 is a different fault on every other Takagi series that documents it, which is exactly why this page is written for the Condensing alone:
Don't confuse this with
One other Takagi Condensing code points at a gas solenoid 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: