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United States · Licensing exam

Washington state plumbing license: L&I plumber certification

Washington calls it a certificate, issued by the Department of Labor and Industries (L&I), and you need one to work in the plumbing trade there. A Washington state plumbing license at journey level takes 8,000 hours as a trainee and a three-part PSI exam.

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Updated October 2026 · Written from official sources, listed at the bottom of this page

Washington plumbing certificates

Certification isn't needed for plumbing outside a building, such as connecting to a city water main or sewer, except on domestic pump and irrigation systems.

CertificateExperience as a trainee
Journey level (PL01)4 years, at least 8,000 hours, with at least 4,000 on commercial or industrial work
Residential (PL02)3 years, at least 6,000 hours
Residential service (PL04)2 years, at least 4,000 hours, the first 2,000 under direct supervision
SpecialtiesPump and irrigation, domestic well, backflow and medical gas piping each have their own certificate

Starting as a plumber trainee

You must be 16 or older. As of October 2026 the trainee certificate costs $60, lasts 12 months, and lets you work under the direct supervision of a certified plumber. To renew it you take 8 hours of approved continuing education a year and send notarized affidavits of your hours.

What's on the Washington state plumbing license exam?

PartItemsTime
Code and general trade knowledge10090 minutes
Waste and vent sizing drawing2590 minutes
Water sizing drawing2590 minutes

The journey level and residential exams follow this pattern. All three parts are closed book, and you need 70% on each. Fail one part and you normally retake all three, after waiting 14 days. You may bring a silent, non-programmable calculator.

As of October 2026, L&I charges $202.10 per exam application and PSI charges $84 for the three-part exam, or $52 for single parts on a retest. If you fail, you send a new application and pay the $202.10 again. After passing you have 90 days to pay the certification fee.

Plumbers from other states

L&I says Idaho has reciprocal certification for journey-level plumbers. Other out-of-state plumbers contact L&I, and can get a temporary permit for $100.30.

Reciprocity in other states →Renewing a Washington certificate →
Sources: Washington L&I · PSI and 2 more. Checked October 2026.

Rules and fees can change, so check the official site before your test.

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