The estimate is on the kitchen counter. $3,200 for a water heater replacement, $4,800 for a pressure regulator and a few related fixtures, $11,000 for a partial repipe of the kitchen and master bath. The plumber who left the estimate seemed competent. The license number is on the document. The two reviews online are positive. Everything looks fine, and the work needs to happen. Before signing, though, there are nine questions worth asking.
The work a plumber does sits behind the walls and under the floors of a home, and the consequences of choosing the wrong one usually show up months or years after the bill is paid. A poorly soldered joint leaks slowly into a wall cavity. An incorrectly vented water heater produces a code violation that surfaces during the next sale. A repipe done with the wrong materials shortens the life of a system that should have lasted decades. Vetting the plumber before the work starts is much cheaper than dealing with the problems a poorly chosen one creates, and the vetting itself isn’t complicated.
A short list of questions, asked early in the conversation, tells most of what a homeowner needs to know.
1. License number, verifiable on the state site
The first question is licensing, and the answer should be specific. Most states license plumbers individually, and the license number is publicly verifiable through the state’s licensing board or contractor registry. A plumber who hesitates to provide their license number, or who provides it but the number doesn’t match an active record on the state’s verification site, isn’t a homeowner’s problem to solve; that’s a vendor to pass on. Active licensing means the plumber has demonstrated technical competence at some baseline, has carried whatever insurance the state requires, and has continued to meet renewal requirements. The license is the floor of professional standing, not the ceiling, but a plumber operating without one is a plumber whose work has no regulatory standing if something goes wrong.
2. Insurance: liability and workers’ comp
The second question covers insurance, and there are two relevant policies. General liability insurance covers damage the plumber causes to the home during the work: a flooded basement from a botched repair, a broken fixture during installation, structural damage from an excavation gone wrong. Workers’ compensation insurance covers injuries to the plumber’s employees while they’re working on the property, which matters because in the absence of workers’ comp, an injured worker can sometimes claim against the homeowner’s policy or the homeowner directly. A reputable plumber will provide certificates of insurance for both policies on request, often through their insurance agent, and the certificates show coverage amounts and policy effective dates.
3. Bonding: the financial guarantee
The third question is bonding. A surety bond is different from insurance: it’s a financial guarantee that protects the homeowner if the plumber fails to complete contracted work or if their work is later found to be defective. Bonding is required for licensed plumbers in many jurisdictions and is voluntary in others. A bonded plumber gives the homeowner recourse beyond civil litigation if something goes seriously wrong with the work. The bond amount is finite (typically in the tens of thousands rather than the hundreds), but it provides a meaningful layer of protection particularly on larger projects.
4. Written estimate, detailed line items
The fourth question is the written estimate. A reputable plumber provides a written estimate before work begins on anything beyond minor service calls, and the estimate should detail the scope of the work, the materials specified, the labor cost, and any contingencies that could change the total. Verbal estimates are not binding and are difficult to dispute later if the bill ends up significantly higher than expected. A plumber who resists putting the estimate in writing, or who provides one too vague to be useful, is signaling something about how they’ll handle the rest of the relationship. The written estimate is also useful for comparing bids across multiple plumbers on the same scope of work.
5. Warranty: parts and labor
The fifth question is warranty. A standard residential plumbing warranty covers parts (typically through the manufacturer’s warranty on whatever is installed) and labor (typically through the plumber’s own warranty, often one year on most work). Longer labor warranties on major work like repipes or water heater installations are sometimes available and worth asking about. The terms matter: a plumber who provides a one-year labor warranty in writing is committing to come back and fix any failure during that period at no charge, and that commitment is meaningful information about how confident they are in the work.
6. References, recent and contactable
The sixth question is references, and the right form is recent ones. A plumber should be able to provide several recent customer references (typically five to ten) for similar types of work, and a homeowner who actually calls those references usually learns more in those conversations than from any other vetting step. The questions to the references are simple: was the work completed on schedule, was the cost in line with the estimate, did problems arise after the work was done, and was the plumber responsive when they did. References that consistently report positive experiences support the hire; references that report missed deadlines, cost overruns, or unresponsive follow-up are information the homeowner can act on before the contract is signed.
7. Who actually does the work
The seventh question is who actually does the work. Many plumbing companies use a mix of licensed plumbers, apprentices, and subcontractors, and the question is what level of supervision the work receives. Apprentices working under direct supervision of a licensed plumber on a residential job is normal and acceptable. Subcontractors handling the work without on-site oversight from the contracting company is less so, particularly when the homeowner contracted with a specific company expecting that company’s standards to apply. Asking who will be on the property and what their credentials are usually clarifies this in a few minutes.
8. Emergency response capability
The eighth question is emergency response capability. For most homeowners, the relationship with a plumber matters most during emergencies: a burst pipe, a sewer backup, a water heater failure on a Sunday night. A plumber who handles emergency calls within reasonable response times, who has after-hours availability, and whose pricing for emergency work is documented in advance is a different vendor than one who only handles scheduled work during business hours. Both have their place; the homeowner deciding which they’re hiring should know which they’re getting.
9. Permits and code compliance for this job
The ninth question covers permits and code compliance for the specific work being contracted. For routine work like fixture replacement or drain cleaning, permits aren’t required and the question is moot. For permit-required work such as water heater replacements, gas line modifications, sewer line repairs, and additions to the plumbing system, the contracted plumber should pull the permits and arrange for the inspections, and the cost of those should be itemized in the written estimate. A plumber who proposes doing permit-required work without permits is exposing the homeowner to insurance and disclosure problems that outlast the immediate cost savings, and that proposal is itself a vetting failure.
Red flags during the vetting conversation
A few patterns in the vetting conversation are worth treating with skepticism:
| Red flag | What it usually signals |
|---|---|
| Pressure to commit before reviewing the estimate | Sales-driven, not work-driven |
| Large cash deposits required up front | Cash flow problems or worse |
| Refusal to put commitments in writing | Disputes will be unwinnable |
| Vague or evasive answers about licensing | Possibly unlicensed or lapsed |
| Same-day-only discount with deadline pressure | Manipulation tactic |
| No certificates of insurance available | Risk transfers to homeowner |
| Estimate without itemized line items | Bill creep risk |
The discount that’s only available if the homeowner commits in the next hour usually isn’t actually a discount.
The vetting investment
The vetting process itself doesn’t take much time. License verification, two phone calls to references, and a review of the written estimate against the scope of work can usually be done in an evening. The investment is small relative to the cost of the project and tiny relative to the cost of dealing with a problem caused by the wrong vendor. Reputable plumbers expect to be vetted and answer the nine questions readily, treating the conversation as a normal part of how the work gets contracted. The estimate on the kitchen counter, signed without these nine questions answered, is a different financial commitment than the same estimate signed after them.
