What a C-4 license allows
CSLB defines the C-4 Boiler, Hot Water Heating and Steam Fitting Contractor classification as follows: “A boiler, hot-water heating and steam fitting contractor installs, services and repairs power boiler installations, hot-water heating systems and steam fitting, including fire-tube and water-tube steel power boilers and hot-water heating low pressure boilers,steam fitting and piping, fittings, valves, gauges, pumps, radiators, convectors, fuel oil tanks, fuel oil lines, chimneys, flues, heat insulation and all other equipment, including solar heating equipment, associated with these systems.” Source: cslb.ca.gov licensing classifications.
C-4 licenses in California by the numbers
As of September 2026, CSLB lists 635 current licenses that include C-4. 80% have workers' comp on file, 16% are filed exempt, and 16 were issued in the last 12 months.
Ownership: 18% sole owners, 73% corporations, 7% LLCs. Suspensions today: 8 for workers' comp, 12 for bonds.
Insurance and bonds a C-4 contractor needs
- $25,000 contractor license bond — required for every active license.
- Workers' comp — A license with employees must carry workers' comp. With no employees you can currently file an exemption; from January 1, 2028 (SB 1455), CSLB will require workers' comp for all active licenses except joint ventures.
- LLC licenses — liability insurance of at least $1 million (up to $5 million by member count) plus a $100,000 employee/worker bond.
- General liability and commercial auto — not required by CSLB for most licenses, but required by nearly every GC, owner and public agency contract.
Carriers underwrite based on the work you actually perform under this classification, your residential/commercial mix, subcontracting and claims history.
Get a quote
Asena Capital Insurance Services compares multiple markets for boiler, hot water heating and steam fitting contractors and requests additional insured endorsements for you when a contract calls for them. Call (858) 925-9555 or request a quote — only your name, phone and email are required. CA License #6008596.