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Good plumber interview questions are about the work: how the candidate diagnoses a problem, explains a repair, handles a surprise inside a wall, and treats a customer's home. Ask every candidate the same questions, score the answers on a sheet, add a paid hands-on test or ride-along, and keep every question job-related.
Key takeaways
- Ask each candidate the same questions in the same order and score the answers the same way.
- Keep every question tied to the job, and avoid questions about age, family, health, religion, national origin and other protected topics.
- Scenario questions show more than résumé questions, because a plumber works alone in a customer's home.
- A short paid test or ride-along tells you what an interview cannot.
- Confirm licensing and the rules for your state before you make an offer.
A plumber you hire will walk into a stranger's house alone, diagnose something hidden, quote it, and fix it. The interview should test those four things, not just the résumé. A note on the law first: the U.S. Equal Employment Opportunity Commission says employers should limit pre-employment questions to what is needed to judge whether a person can do the job, and that employers are prohibited from asking about disability before making an offer. Avoid questions that could reveal age, race, sex, religion, national origin, disability or family plans. State and local rules vary, so this is general information and not legal advice. Each item below gives the question, why it matters, what a strong answer sounds like and a red flag. If you are building the company around the hire, our plumbing business guide and plumbing industry page cover the rest.
1. Walk me through the last three plumbing jobs you did start to finish.
Why it matters: it separates the person who ran a job from the person who handed over tools. Strong answer: specifics such as the fixture, the pipe material, what went wrong and how they fixed it, using the right names for parts. Red flag: vague answers, "we" for everything, or no job they can describe in detail. Ask a follow-up about the part of the job they personally did. Take notes on the sheet while they talk, since memory blurs after the fourth candidate.
2. What license, registration or training do you hold, and what work does it cover?
Why it matters: plumbing licensing rules differ by state, and what a person may do depends on their level. Strong answer: names the credential, the issuing body, the level, and what they can do alone versus under a licensed plumber. Red flag: a fuzzy answer, a credential from another state with no plan to transfer it, or "I've never needed one." Verify with the state licensing agency before the offer. Our guide on how to become a licensed plumber explains the usual pathway, and your state board has the final word.
3. A customer says there's no hot water. What do you ask on the phone and what do you check first?
Why it matters: it shows diagnostic order. Strong answer: asks the type of heater, how old it is, whether it's one fixture or all, and checks the simple things first (pilot, power, breaker, thermostat, relief valve) before opening anything up. Red flag: jumps to "replace the heater" without a question. Listen for whether they think about safety around gas and a leaking tank. A good candidate also tells the customer what they'll do before they do it.
4. How do you find a leak you can't see without tearing up more than you have to?
Why it matters: hidden leaks mean damage to a customer's finished space. Strong answer: shutting off fixtures to isolate the line, watching the meter, listening, using a moisture reader or camera, and cutting the smallest opening, then patching it. Red flag: opens the wall first and asks questions later. Ask what they tell the customer about drywall repair before they cut, and who handles it. This question reveals whether they treat a house like a work site or like a home.
5. Tell me about a job that turned out bigger than you quoted. What did you do?
Why it matters: every plumber meets corroded pipe or a bad past repair. Strong answer: stopped, showed the customer the problem, explained the options and cost, got approval before continuing, and noted it on the ticket. Red flag: did extra work and billed it without asking, or quietly ate the cost and never told the office. You are hiring someone whose decisions become your reputation, so listen for whether the customer was in the loop.
6. Explain a clogged main line to me as if I'm a homeowner.
Why it matters: customers decide based on the explanation. Strong answer: plain words, no jargon, a picture in the customer's head ("this pipe runs from your house to the street"), and a clear statement of what's known and what isn't. Red flag: condescension, jargon, or a hard sell. Try a role-play where you play the customer and push back on a recommendation. How they respond to "that sounds expensive" tells you how they'll handle the real thing in someone's kitchen.
7. Describe a time you recommended less than the customer expected to buy.
Why it matters: a plumber who only sells up damages repeat business. Strong answer: an example where a repair was enough and they said so, or where they told a customer a fixture could last another year. Red flag: cannot think of one, or talks about commission as the goal. If you pay a spiff or commission, say so in the interview and ask how the candidate separates the customer's need from their own payout. It is a fair question about judgment, and it sets expectations early.
8. How do you behave when you're alone in a customer's home?
Why it matters: trust is part of the product. Strong answer: shoe covers or drop cloths, a call before arrival, cleaning up, not wandering, handling pets and kids' spaces with care, and telling the customer when something gets damaged. Red flag: dismisses the question or blames customers. Ask for a story about a time they damaged something and what they did. Honest candidates have one and tell it straight. That honesty matters more than a spotless record.
9. What are the safety steps you take before opening a line or working near gas or a water heater?
Why it matters: injuries and flooding come from skipped steps. Strong answer: locates and tests the shutoff first, relieves pressure, checks for gas smell and venting issues, uses the right PPE, and knows when to stop and call for a licensed gas fitter or the utility. Red flag: shortcuts described as a point of pride. Check your state's rules on who may work on gas lines. Write the answer on the sheet and compare it with your own safety policy.
10. Tell me about a mistake you made on a job and how you fixed it.
Why it matters: everyone cuts the wrong line eventually. Strong answer: owns the mistake without blame, describes how it was repaired, what the customer was told, and what they changed afterward. Red flag: "I don't make mistakes" or a story where someone else is at fault. Pay attention to whether they called the office right away. A team runs better when problems surface in minutes, not after the customer complains.
11. How do you document a job: photos, notes, invoices?
Why it matters: unrecorded work turns into disputes and missed billing. Strong answer: before-and-after photos, a clear description of what was done, parts used, and a ticket closed the same day. Comfortable with a phone or tablet app. Red flag: "the office figures it out." Tell the candidate which system you use. If you run a custom setup, our custom CRM service shows how job notes, photos and invoices can sit on one record, and a candidate who already documents carefully will adapt quickly.
12. What tools do you own, and what do you expect the company to supply?
Why it matters: it avoids a day-one surprise on both sides. Strong answer: a clear list of hand tools, specialty tools and their condition, and honest expectations about camera, jetter or press tools. Red flag: arrives expecting everything supplied or can't list their own. Put your tool policy in writing before the interview, and do not ask a candidate to buy tools as a condition of an offer without checking your state's wage rules.
13. This job involves driving a company vehicle and an on-call rotation. Can you do that?
Why it matters: it states the real requirements of the role. Strong answer: a direct yes or no, plus questions about how the rotation works and how on-call time is paid. Red flag: evasion. Ask this exact question of every candidate and describe the job's real requirements, not guesses about a person's circumstances. Do not ask about children, childcare or plans. If you need a driving record check, get the candidate's written consent where the law requires it and follow your state's rules and your insurer's requirements.
14. Run a short, paid hands-on test.
Why it matters: talking about soldering is not soldering. Strong answer: a clean, correctly sequenced job in the time allowed, with tools handled safely. Set up a mock-up board: replace a faucet or angle stop, make a few joints, or assemble a small rough-in section. Give the same test and the same time to every finalist. Red flag: sloppy joints, no leak check, no cleanup. Pay for the time. Ask your payroll provider or attorney how your state treats trial work, since unpaid trials can raise wage problems.
15. Do a ride-along on a real service call.
Why it matters: you see how they greet, diagnose and talk to a customer. Strong answer: introduces themselves, asks before touching, explains what they see, and cleans up. Pair the candidate with a lead tech, tell the customer a new technician is observing, and pay for the time. Red flag: talks over the customer, ignores the lead's instructions, or leaves a mess. Ask your insurance broker whether a non-employee on a job site is covered before you schedule a ride-along.
16. Ask for two references, then ask what they'd like to ask you.
Why it matters: a former supervisor knows things the interview cannot show. Strong answer: offers references from recent work and understands why you ask. On the reference call ask the same job-related questions: reliability, quality, how they treat customers, whether the employer would rehire. Then ask the candidate what questions they have. Red flag: no questions at all, or only questions about pay and time off. The best candidates ask how jobs are assigned, who they report to and how mistakes are handled.
Where to start
If you only change three things, write down questions 3, 5 and 8 and ask them of every candidate, score each answer on a sheet, and add the paid test in item 14 for your top two. Those three questions cover diagnosis, honesty with the customer and behavior inside a home, which is where bad hires cost you. Keep applicant notes in one place, such as a spreadsheet or your CRM, so you compare the same facts and not your memory. Before an offer, verify the license with the state, and have an employment attorney or your state agency check your hiring paperwork.
Frequently asked questions
Can I ask a plumber candidate if they have a license?
Yes, it is job-related. Ask which credential they hold and what work it covers, then verify it with your state licensing agency. The rules differ by state.
Should every candidate get the same questions?
Yes. Asking the same questions in the same order and scoring them on a sheet makes the comparison fair and gives you a record of why you chose who you chose.
Is it legal to ask about a candidate's physical ability to lift or crawl?
The EEOC's guidance on pre-offer disability questions says an employer may ask whether applicants can perform job functions with or without reasonable accommodation, so describe the duties and ask every applicant the same way. Avoid asking about health or disability itself before an offer, and check your state's rules.
How long should a plumber interview take?
Plan 30 to 45 minutes of questions for a first round. Reserve the hands-on test and ride-along for finalists so you do not spend hours on every applicant.
Sources
General information for service-business owners, not legal, tax or financial advice. Rules vary by state; check with a qualified professional for your situation.