The Spark Plug (3B1A-3/8NP) is a dual-function ignition component engineered for Mr.Steam CU Series Steam Shower Generators. This probe generates the high-voltage spark needed to ignite the burner, then immediately shifts roles to serve as a flame-sensing probe, confirming successful ignition and monitoring the flame throughout operation. If ignition fails or the flame drops out, this probe helps trigger a safe automatic shutdown, protecting the commercial installation from unsafe combustion conditions. Reliable ignition sensing is critical in commercial steam room operation, where consistent startup performance keeps the system running on schedule without unexpected service calls. Constructed to withstand the sustained heat of the combustion chamber, this genuine Mr.Steam replacement part restores dependable startup and safety monitoring after a worn or failed probe. Straightforward to install, it's an essential component for keeping a commercial steam system's ignition and safety circuit performing as designed.