Boiler, Hot Water Heating and Steam Fitting Contractor Insurance in California (C-4)

What the C-4 license covers

The CSLB’s definition

“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.”

The large C-4 claims are property damage: a boiler or line that fails after you finish, scalding water, a burst pipe in a commercial building, or a fire from a fuel line. Those land on the completed-operations part of your general liability. Many commercial clients also ask for coverage on the equipment while it is being installed.

The C-4 coverage stack

General Liability — with completed-operations coverage for system failures after the job
Workers’ Compensation — rated 3726, with 5183/5187 for steam fitting
Commercial Auto — service vans and trucks carrying pipe and parts
Inland Marine — installation floater for boilers and parts before the owner accepts them
CSLB license bond — the $25,000 bond every C-4 license needs
Excess & Umbrella — commercial and industrial contracts often require $2M or more

C-4 requirements

What California requires of a C-4 licensee

Requirement	What applies to C-4 boiler contractors
Contractor’s license bond	A $25,000 bond is required to activate and keep the license. LLC licensees also need a $100,000 LLC employee/worker bond. How the bond works
Workers’ compensation	Required now if you have even one employee. With no employees you can file a CSLB exemption, but that option ends for every classification on January 1, 2028. Check your requirement
General liability	Required by the CSLB only for LLC licensees (at least $1 million). General contractors and owners require it anyway, usually with additional insured status.

Workers’ comp class codes and 2026 rates

Class code	Description	Advisory rate per $100 payroll
3726	Boiler installation, service or repair, steam or hot water	$2.02
5183	Steam and pipe fitting, workers paid under $35.00/hr	$5.72
5187	Steam and pipe fitting, workers paid $35.00/hr or more	$2.73
5184	Steam pipe or boiler insulation	$2.88

Source: WCIRB California, approved September 1, 2026 advisory pure premium rates and classification descriptions. These are benchmark loss costs, not quotes: each carrier files its own rates, and your experience mod and credits adjust the final premium.

Boiler installation and service has its own code, 3726. Steam fitting and piping fall under the plumbing codes, which split at a $35 hourly wage. Insulating steam pipes and boilers is a separate code again. Keep payroll records by type of work so each hour lands in the right code at audit.

Code 3726

boiler installation and service, separate from plumbing

$35/hr

the wage line that splits the steam fitting codes

WC by 2028

every C-4 needs a policy, employees or not

Common questions

C-4 coverage, answered

What is the workers’ comp class code for boiler contractors in California?

Boiler installation, service or repair is code 3726, with a 2026 WCIRB advisory rate of $2.02 per $100 of payroll. Steam fitting and piping are rated as plumbing: 5183 for workers paid under $35.00 an hour ($5.72) and 5187 for $35.00 or more ($2.73).

Is general liability required for a C-4 license?

Only for LLC licensees, which must carry at least $1 million. Sole proprietors and corporations aren’t required to by the CSLB, but most general contractors and public agencies will require it before you start.

Does my insurance cover a boiler I installed if it fails later?

Damage to other property from a failure after the job is usually covered by the completed-operations part of general liability, as long as the policy was in force and has no exclusion that applies. Fixing or replacing your own faulty work is usually not covered.

Do boiler contractors need workers’ comp with no employees?

Not yet. A C-4 licensee with no employees can file the CSLB exemption until January 1, 2028, when the exemption ends for every classification. Any employee means you need a policy now.

Boiler, Hot Water Heating and Steam Fitting Contractor Insurance in California

The CSLB’s definition

The C-4 coverage stack

What California requires of a C-4 licensee

Workers’ comp class codes and 2026 rates

C-4 coverage, answered

Get a C-4 quote that fits the work