Hiring a plumber in Ontario without checking their credentials is a risk most homeowners can't afford. Faulty plumbing work can void your home insurance, result in costly water damage, or even create health hazards from improper gas or drain connections. The good news is that Ontario has clear, publicly accessible systems that let you verify a plumber's licence in minutes — if you know where to look. This guide walks you through exactly what to check and why each step matters.
Why Licencing Matters for Plumbing Work in Ontario
In Ontario, plumbing is a regulated trade under the Ontario College of Trades (OCOT), now administered through the College of Trades and Apprenticeship Act and overseen by the Ministry of Labour, Immigration, Training and Skills Development. Plumber (229A) is a compulsory trade, which means anyone performing plumbing work for compensation must hold a valid Certificate of Qualification. This isn't a technicality — it is the law.
Beyond the legal requirement, a licensed plumber has logged thousands of hours of apprenticeship, passed a provincial exam, and is accountable to a regulated body. An unlicensed contractor has none of that oversight. If something goes wrong, you may have little legal recourse and your insurer may deny a claim linked to work performed without proper credentials.
Step 1: Verify the Plumber's Certificate of Qualification Through OCOT
The most important verification step is confirming that the plumber holds a valid Certificate of Qualification (C of Q) for the trade of Plumber (trade code 229A). Here is how to do it:
- Ask the plumber directly for their Certificate of Qualification number. A legitimate tradesperson will provide this without hesitation.
- Visit the Ontario College of Trades member directory on the official OCOT website (ontario.ca or the college's verification portal) and enter the certificate number or the individual's name to confirm the credential is active and has not expired.
- Check that the trade listed on the certificate matches the work you are hiring for. A journeyperson plumber's certificate covers water supply, drain, waste, and vent systems. Gas work is a separate certification — more on that below.
If a plumber cannot produce a certificate number, or if the number does not appear in the registry, treat that as a serious red flag and look for another contractor.
Step 2: Confirm WSIB Coverage
The Workplace Safety and Insurance Board (WSIB) provides workers' compensation coverage in Ontario. Before any tradesperson sets foot in your home, you should confirm they have valid WSIB coverage. Without it, you could be held financially liable if a worker is injured on your property.
- Ask the plumber or their company for a WSIB Clearance Certificate. This document confirms that their account is in good standing and that premiums are paid up to date.
- You can independently verify a clearance certificate using the WSIB's online verification tool at wsib.ca. Enter the contractor's account number to get a real-time confirmation.
- Clearance certificates have an expiry date — confirm it covers the dates your work is scheduled.
Step 3: Check for Gas Licensing if Applicable (TSSA)
If your project involves any gas lines, gas appliance connections, or gas-fired water heaters, plumbing credentials alone are not sufficient. Gas work in Ontario is regulated by the Technical Standards and Safety Authority (TSSA). A contractor performing gas work must hold a valid Gas Technician (G1 or G2) licence issued by the TSSA.
You can verify a gas technician's licence through the TSSA's licence verification tool at tssa.org. Simply search by the technician's name or licence number. Never allow gas work to proceed without confirming this separately from the plumbing licence — they are two distinct authorisations.
Step 4: Ask for Proof of Liability Insurance
In addition to WSIB, any reputable plumbing contractor should carry general liability insurance — typically a minimum of $2 million in the GTA market. This protects you if their work causes property damage, such as a pipe failure that results in flooding. Ask for a certificate of insurance directly from their insurer, not just a copy handed to you by the contractor, so you know it is current.
Step 5: Verify the Business and Get a Written Contract
Before signing anything, confirm the business is registered in Ontario. You can search business names through the Ontario Business Registry at ontario.ca/page/ontario-business-registry. A properly registered business will also provide a written quote that breaks out labour, materials, and HST at 13% as a separate line item. If a contractor offers to do the work for cash without HST, that is a strong indicator they are operating outside the law.
Always insist on a written contract that specifies the scope of work, materials, payment schedule, start and completion dates, and warranty terms. Verbal agreements offer very limited protection under Ontario law.
Quick Checklist Before You Hire a Plumber in Ontario
- OCOT certificate: Confirm trade code 229A is active in the registry
- WSIB clearance: Verified online at wsib.ca
- TSSA gas licence: Required for any gas-related work, verified at tssa.org
- Liability insurance: Certificate from the insurer, minimum $2 million recommended
- Ontario Business Registry: Business is properly registered
- Written contract with HST: 13% HST shown as a separate line
What Happens if You Hire an Unlicensed Plumber?
The consequences can be significant. Permits pulled for work completed by an unlicensed contractor may not be approved by your municipality. Home insurance claims related to plumbing failure may be denied if the work was not performed by a licensed tradesperson. In the GTA, where property values are high, the financial exposure from a major water damage event makes the few minutes it takes to verify credentials well worth the effort.
Ontario's regulatory framework exists to protect homeowners. Using it is simply good practice — and it costs nothing.