Washington Plumbing Specialty Licenses — PL02, PL04, PL03, PL03A, PL30, and MG01 Explained

Most plumbers in Washington focus on the journey-level PL01 because it carries the broadest scope. But L&I issues six specialty certifications, each with different hour thresholds, supervision ratios, and work restrictions. Picking the wrong one — or not knowing a specialty exists — can lock you into residential-only work or force you to start over with a different hour track.

The Six Washington Plumbing Certifications

Every certification below is issued by the Department of Labor & Industries under RCW 18.106 and WAC 296-400A. The key differences come down to scope, required hours, and who can supervise you.

PL01 — Journey Level Plumber

The full-scope credential. PL01 holders can work on residential, commercial, and industrial plumbing with no restrictions. Requirements: 8,000 hours over at least four years, with a minimum of 4,000 hours in commercial or industrial work. After meeting the hour threshold, you sit for the three-part PSI exam (general knowledge, waste/vent sizing, water pipe sizing — 70% passing score on each section).

PL02 — Residential Specialty Plumber

PL02 limits you to single-family dwellings, duplexes, and apartment buildings up to three stories. The trade-off is a lower hour requirement: 6,000 hours over at least three years, all under a PL01 or PL02 supervisor. On residential construction sites, the current temporary supervision ratio is 1:3 through December 31, 2028 (one certified plumber to three trainees). If your career plan is strictly residential, PL02 gets you certified a year sooner than PL01.

PL04 — Residential Service Plumber

PL04 is the narrowest residential credential. It covers only service, repair, or replacement of existing fixtures and piping outside the interior wall or above the floor in single-family homes and duplexes. No new construction. The requirement is 4,000 hours over two years. The first year and 2,000 hours must be under a PL01 or PL02 supervisor; the second year can be under another PL04 holder.

L&I normally uses a 1:1 supervision ratio for residential service; a temporary 1:3 ratio applies to like-in-kind residential service through December 31, 2028, after which it reverts to 1:1.

PL03 — Pump and Irrigation Specialty

PL03 covers installation, maintenance, and repair of equipment used to acquire, treat, store, or move water for drinking or irrigation. This is a combination credential: trainees must simultaneously hold both a plumber trainee card and an electrical trainee card (ET00), because pump systems involve electrical connections. The hour requirement is 4,000 hours over two years.

The current supervision ratio is 1:3, also expiring December 31, 2028 (shifting to 1:2).

PL03A — Domestic Well Specialty

PL03A covers installation and repair of equipment used to acquire or treat drinking or irrigation water using a pump not exceeding 100 GPM or 7.5 HP. It requires 2,000 hours over one year, direct supervision by an appropriate certified plumber, and an electrical trainee card. The current supervision ratio is 1:3 through December 31, 2028, shifting to 1:2 thereafter.

PL30 — Backflow Specialty

PL30 is maintenance and repair of existing backflow prevention assemblies within a building's footprint. There is no hour-based training requirement. Instead, you need a valid Backflow Assembly Tester (BAT) certificate issued by the Washington Department of Health. Supervision is strict: 1:1 for 100% of on-site time.

MG01 — Medical Gas Piping Installer

MG01 is not a standalone certification — it is an endorsement that sits on top of an active PL01 journey-level license. It authorizes installation of medical gas and vacuum piping systems (oxygen, nitrous oxide, medical compressed air) in healthcare facilities. You must complete 32 hours of L&I-approved medical gas training. Like PL30, the supervision ratio is 1:1 for 100% of time on-site.

Choosing the Right Track

The decision comes down to your long-term scope. If you plan to do commercial work or eventually become a contractor, PL01 is the only path that keeps all doors open. PL02 saves a year but limits you to residential work; it does not cover commercial and industrial projects. PL03A is the fastest track in this list at one year, while PL04 is the fastest residential credential but limits you to service work on existing systems.

For a side-by-side breakdown of hours, fees, and the step-by-step application process for each classification, the Washington Plumber License Guide maps every route from trainee card through contractor registration.

See more Washington guides →