California CSLB classification
Hydronics and steam for commercial buildings. Classes, paperwork, bonding and business setup handled by one team, in English or Spanish.
✓ Licensed in as little as 90 days. Payment plans available. Se habla español.
What the license covers
The C-4 classification covers installing, servicing and repairing low-pressure and high-pressure boilers, hot water heating systems, steam fitting, and the piping, controls and accessories that serve them.
Commercial building owners, schools, hospitals, industrial facilities, and multifamily properties.
Boiler work is technical, code-heavy and inspection-driven, which limits competition and supports service contracts on top of installation work.
CSLB requirements
Four years of journeyman-level experience in boiler, hot water heating and steam fitting work, verified by someone who can attest to it. Apprenticeship, technical training and certain degrees can substitute for up to three of those years.
You'll also need a valid Social Security number or ITIN to file the application.
The CSLB Law & Business exam, plus the C-4 trade exam. Both are taken at a CSLB testing center.
Live Scan is required for every applicant and qualifier. Prior convictions don't automatically disqualify you, but they must be disclosed.
Filed with the CSLB before your license is issued. You pay an annual premium to a surety, not the full bond amount.
As of 2026 nearly all licensees must carry workers' comp coverage, including many contractors who previously qualified for the no-employee exemption.
Course options
Every course covers the Law & Business exam and your C-4 trade exam, updated for 2026 code.
8-week online
$895
For contractors who already know the trade and want to test fast.
Most students pick this
4-month online
$1,195
The balance of time and coaching that gets the most people licensed.
7-month online
$1,495
For anyone working full time who needs room to study around the job.
Payment plans available on every course. Not sure which fits? Call and we'll tell you straight.
Related classifications
Most contractors end up holding more than one. These are the classifications that most often sit alongside a C-4.
See all 44 CSLB classifications →
Straight answers
Plumbing contractors handle some water heating. Boilers, hot water heating systems and steam fitting are the C-4 scope.
Hydronic radiant heating is within the C-4 scope.
Pressure vessels may be subject to separate state inspection requirements depending on the equipment.
Most students are licensed in about three months. The timeline depends on how quickly you finish the course, when you schedule your exams, and current CSLB processing times.
Yes. We complete and file everything — the application, experience verification, bond and insurance documentation. Incomplete applications are the number one cause of delay, so we check every line before it's submitted.
Sí. Todo nuestro equipo es bilingüe. Las clases, la ayuda con la aplicación y todas las actualizaciones están disponibles en español.
Ready when you are
A C-4 lets you pull permits, take jobs over $1,000, and bid the boiler, hot water heating and steam fitting work you're already good enough to do. Thirty thousand contractors have done it with us.
