Plumbing Contractor License in Washington: Requirements, Qualifier, Bond and Exams

Statewide, and it is a distinct business license.

As of July 2021, you must be licensed as a Plumbing Contractor with L&I to advertise, offer to do work, submit a bid, or perform plumbing work, and only licensed plumbing contractors may employ certified plumbers on plumbing jobs.

The requirement reaches general contractors too: a Washington general contractor that wants to do plumbing work must also hold the plumbing contractor license, with a bond separate from its contractor registration bond.

L&I — the Washington State Department of Labor & Industries — issues the license, the same agency that runs the Plumber Certification Program the state requires plumbers to certify under.

For businesses, the L&I pages we read show a single class: the Plumbing Contractor license.

The contrast inside the same agency is useful context: HVAC contractors register with L&I as specialty contractors, with no exam or qualifier and a $150.20 fee, while plumbing businesses have held this separate Plumbing Contractor license since July 2021.

On the worker side, L&I certifies Journey Level (PL01) plumbers and the specialty certificates — Residential (PL02), Pump & Irrigation (PL03), Domestic Well (PL03A), Residential Service (PL04) and Backflow (PL30), the last requiring a Department of Health Backflow Assembly Tester certificate — plus a Medical Gas piping installer (MG01) endorsement for journey level plumbers.

You can check a registration or certificate with L&I's Verify a Contractor, Tradesperson, or Business tool.

Washington's qualifier is the designated plumber: the license requires an assigned designated plumber holding an L&I plumber certification.

Our research did not confirm which certification level L&I requires that plumber to hold, so ask L&I before you staff the role.

For scale, the general certification is a long road: Journey Level (PL01) takes four years or more (at least 8,000 hours) working as a plumber trainee under a certified journey level plumber, including at least 4,000 hours on commercial or industrial work.

The record-keeping behind those hours is strict: trainees must be at least 16, hold a $60 trainee certificate valid 12 months, work under direct supervision of a certified plumber, and report their hours yearly on notarized affidavits — and hours from out-of-state employers or apprenticeship programs do not count.

The full trainee-to-journey ladder sits in our Washington plumbing license guide for individuals.

The license steps in the L&I page we read are the bond, the insurance and the designated plumber — no separate contractor exam appears among them.

The exams in the record belong to the worker certifications your designated plumber and crew hold: Washington plumber exams are administered by PSI and based on the 2015 Uniform Plumbing Code with Washington amendments, and the journey level and residential exams are closed book.

A candidate who fails must file a new $202.10 application and wait 2 weeks (14 calendar days) before scheduling another date with PSI.

Our research did not find a separate business-and-law exam for Washington plumbing contractors; confirm the current exam lineup with L&I before you plan study time.

The license carries two money requirements: a $6,000 surety bond — or an assigned savings account in the same amount — and $250,000 liability insurance.

The plumbing bond sits apart from the contractor registration system: a general contractor that adds plumbing work holds the plumbing contractor license with a bond separate from its contractor registration bond.

For scale, those registration bonds are $30,000 for general contractors and $15,000 for specialty contractors since July 1, 2024, and the registration's insurance minimums are $200,000 public liability plus $50,000 property damage, or a $250,000 combined single limit — the plumbing license's $250,000 is its own requirement.

HVACHires also keeps a guide to contractor license bonds and insurance.

This is the gap in our research: the plumbing contractor license fee, the renewal cycle and the deadline for replacing a designated plumber were not confirmed.

Where to look: RCW 18.106 and L&I's rules in WAC 296-400A — read them or ask L&I before you budget.

What the record does price is the people and paperwork around the license: the designated plumber's certification costs $202.10 for the exam application and then a $242.70 certification fee at journey level, residential or residential service.

Certifications renew on the holder's birthday every 3 years with 24 hours of continuing education — at least 12 hours of plumbing code and 4 hours of industry-related electrical for PL01, PL02 and PL04.

For the plumbing contractor license itself, our research found no reciprocity agreement in the L&I pages we read — ask L&I before you rely on an out-of-state credential.

The reciprocity on record belongs to the worker certificates your crews hold: Washington has reciprocal certification with Idaho for journey level plumbers.

Plumbers certified elsewhere must pass the Washington exam, though they can ask for a one-time 120-day temporary permit costing $100.30 while they wait.

Note too that trainee hours from out-of-state employers or apprenticeship programs do not count toward Washington certification — a constraint when you relocate staff.

This is a gap in our research, not a settled rule: we did not confirm a Washington deadline for replacing a designated plumber, or what notice L&I expects.

What L&I's licensing page does establish is that the license requires an assigned designated plumber, alongside the $6,000 bond and the $250,000 insurance.

Each plumber certification also renews on its holder's birthday every 3 years — so, on our reading, a designation sits on a credential with its own renewal clock.

Ask L&I what your business may and may not do while it is between designated plumbers, and read HVACHires' qualifying agent guide for how these arrangements work.