CSLB License Check: How to Verify a California Plumber (C-36)
Two minutes on a state website can save you from the worst hiring mistake a homeowner can make. Every legitimate plumbing contractor in California is licensed by the Contractors State License Board (CSLB), and the board's public lookup tool lets you verify anyone claiming to be one. Here is exactly how to do it, and what everything on the screen means.
Why the license check matters
Under California law, any construction or repair job — including plumbing — where labor and materials combined exceed $1,000 must be performed by a licensed contractor. (This threshold was raised from the long-standing $500 limit in 2025.) An unlicensed person taking on a bigger job is committing a crime, and you lose important protections: no contractor bond to claim against, likely no insurance, and no CSLB complaint process with real teeth.
Worse, if an unlicensed worker is injured on your property, you as the homeowner may be treated as the employer — with the liability that implies.
What a C-36 license means
CSLB licenses are divided into classifications. C-36 is the plumbing contractor classification. It covers installation and repair of water, gas, and drainage systems: supply piping, fixtures, water heaters, drain and vent systems, and related work under the California Plumbing Code. A general contractor (B license) can include plumbing within a larger multi-trade project, but for a standalone plumbing job — a repipe, a sewer line repair, a water heater swap — you want a C-36.
How to run the check on cslb.ca.gov
- Go to cslb.ca.gov and open the license check / "Check a License" tool.
- Search by the license number printed on the plumber's ad, truck, or estimate. Searching by business name works too, but the number is unambiguous.
- Confirm the business name matches exactly the name on your estimate or contract. A license belonging to a different entity does not protect you.
- Check the status: it should say active. Suspended, expired, or revoked means walk away.
- Verify the C-36 classification is listed.
- Confirm the $25,000 contractor bond is on file and current.
- Look at workers' compensation: the company must either carry a policy or have a certified exemption stating it has no employees. If a "one-man" exempt contractor shows up with a crew, that is a serious red flag.
- Scan for disciplinary actions or pending complaints in the record.
Red flags the lookup can reveal
- A license number that belongs to someone else — license "borrowing" is a known scam pattern.
- A brand-new license following a revoked one under a different business name.
- A workers' comp exemption combined with obvious employees on site.
- No license number at all on ads or business cards — California requires contractors to display it, and its absence usually means there isn't one. More warning signs in our guide to plumber red flags and scams.
What about small jobs under $1,000?
An unlicensed handyman may legally perform plumbing work only if the entire job, labor and materials included, stays under $1,000 — and they must tell you they are unlicensed. For a $150 faucet washer swap, that can be fine. But note that jobs cannot be artificially split into pieces to duck the limit, and anything involving gas, permits, or structural drainage belongs with a licensed C-36 regardless of price.
Check done — now compare
A valid license is the entry ticket, not the finish line. Once you have two or three licensed candidates, compare their written estimates carefully — see our checklist for hiring a plumber in California. Or save yourself the search: describe your job on Plumber Comparator and request your free quote, and a licensed local plumber will contact you directly.
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