What interview questions should you ask a plumber? (with good answers)
A question bank for owners and service managers: technical questions with the answers to listen for, customer and behavioural questions, a practical task, red flags and a scoring method.
The questions to ask when hiring a plumber fall into three groups: technical questions with right answers, customer and behavioural questions where you are listening for judgment, and a practical task the candidate performs in front of you.
This page gives you the bank for each group, with the answer a competent plumber should give, the red-flag answers, and a simple way to score candidates against each other.
Before the interview
Write the questions before the candidate is in the room — and write them from your own job description.
The duties you listed are the test blueprint: if the posting says residential service and repair, the interview asks about dwellings, drains and fixtures, not boiler rooms.
Before an offer you may ask about an applicant's skills, education, work history and required certifications and licences, and you may ask them to describe or demonstrate how they would do the job's tasks — that is what the practical section below is for.
If the posting isn't written yet, start from our plumber job description template, then build the question sheet from it.
State the job's physical requirements and ask whether the candidate can meet them.
The EEOC's own examples are lifting a certain amount of weight and climbing ladders; if your work means crawl spaces, trenches or heavy fixtures, the same principle applies — say what the job demands and ask directly whether the candidate can do it.
Know what you may not ask before an offer.
Not about past job injuries or workers' compensation history — keep "ever hurt your back under a house?" off the sheet, out of the phone screen and out of small talk.
You may ask about current illegal drug use, but not about lawful prescription medication.
And in several states and D.C. salary-history questions are banned — the ones this research verified are Virginia, Hawaii, Rhode Island, D.C. and California, plus others it did not check, so treat that as a floor rather than the full list.
The safe habit everywhere: post the pay range and ask what the candidate is looking for.
Which of these rules binds you depends partly on your size.
Federal EEO laws — Title VII and the ADA — cover private employers with 15 or more employees; the age discrimination law covers those with 20 or more; the Equal Pay Act covers virtually all employers.
A shop with 4 to 14 employees is still covered by the Immigration Reform and Control Act's national-origin and citizenship discrimination rules, which the U.S. Department of Justice enforces.
State laws often reach smaller employers than the federal ones, so check your state's rules too.
Run the same questions, in the same order, for every candidate.
You will compare answers fairly, and your notes will still make sense by the time the last interview of the week is done.
The full sequence — sourcing, licence verification, pay, onboarding — is our guide to how to hire a plumber; this page picks up at the interview itself.
Which technical questions test real plumber skill, and what are good answers?
A homeowner calls: water is pooling around the base of the water heater. Walk me through that call.
What to listen for: Questions before conclusions: where exactly the water shows, whether it is the tank itself or a fitting above it, and the age of the heater.
A competent plumber diagnoses before naming a part or a price — 'it's the tank, I'll bring one out tomorrow' with no questions asked is a guess with your name on the invoice.
Listen also for the honest conversation when the tank is the problem: repair talk that delays an end-of-life replacement costs you a second call and an angry customer.
A customer's main line backs up and two fixtures are overflowing. What do you do first, and how do you make sure it doesn't happen again?
What to listen for: Isolation first — one branch or the whole house — then the cleanout, then the cable.
The answer that separates the plumber from the drain operator is the second half: a strong candidate wants eyes on the line, a camera, to learn why it stopped up, because roots, a sag and a bad fitting all 'clear' the same way and come back on your warranty. 'It drains now, that's fixed' is a callback generator.
Copper, PEX, CPVC — how do you decide what to run, and how does each join?
What to listen for: The joining methods stated cold — soldered joints, or mechanical press and expansion fittings, or solvent cement — without hesitation; that is hands knowledge, not brochure knowledge.
The stronger half is judgment: what the application needs, what the manufacturer's instructions require, and whether the material is allowed where you work.
Local plumbing code can differ from the model code, and a strong candidate confirms with the local authority having jurisdiction instead of assuming.
A plumber who sells one material for every job is quoting, not plumbing.
Have you run gas lines? Describe the last one.
What to listen for: The whole sequence — what the run serves, how it was sized and supported, and the pressure test at the end — with the test described as the point of the job rather than a formality.
Then flip it: ask what your city or state requires before someone runs gas on your trucks.
Licensing varies by state and often by city, so confirm the gas-work requirement with the issuing board or your city rather than assuming from the last hire's paperwork.
What plumbing licence do you hold, and what can you do unsupervised under it?
What to listen for: The exact licence — journeyman, master, or whatever your state's ladder calls the tier — and the board that issued it, named without looking anything up.
A strong candidate knows the scope as well as the card: what they may run alone, what needs another licence's sign-off, and what they have never touched.
Out-of-state candidates should ask about recognition before assuming their card transfers.
Whatever the answer, you verify it through the issuer's own record — the state board's public lookup for a state licence, or the city or county where licensing is local — never a photo of a card.
Which customer and behavioural questions matter most?
Explain to me — as if I'm the customer — why there's no hot water and what it costs to fix.
What to listen for: Plain language, options with trade-offs, and a price stated without apology.
Your plumber delivers bad news in people's kitchens; listen for whether they check that the customer followed them or just recite.
Jargon without translation is a bad sign, and so is hiding the number until the invoice.
Tell me about the messiest job you've finished — ceiling open, floor up. How did you leave the house?
What to listen for: Protection and closure described unprompted: covers down, photos of the opened wall before it closes, the finished work walked through with the customer.
Plumbing opens ceilings, cuts walls and puts water where water shouldn't be — the candidate who volunteers how they contain that is protecting your reviews. 'The drywaller fixes it after' with no system around it is how a repair turns into a damage argument.
Tell me about the angriest customer you've ever had to deal with.
What to listen for: A specific story, told calmly: what set it off, what the candidate did, how it ended.
You want de-escalation and documentation, not victory.
A candidate who tells every story as 'the customer was unreasonable' will recreate that conversation in your customers' homes.
Tell me about a callback — a job you did that failed or wasn't right the first time.
What to listen for: Ownership without self-flagellation, and a change that followed: what they now check that they didn't before.
Everyone in this trade has callbacks; a candidate whose every story is someone else's fault is telling you how they'll describe your shop's work to your customers.
Why did you leave your last contractor, and what would the owner say about your work?
What to listen for: A checkable answer: names, the kind of work they ran, a reason you can confirm on a reference call.
Vague on names usually means vague on history.
Ask what their boss would call their weakness — then actually call and compare.
What practical task should a plumber candidate do?
Solvent-weld this joint at the bench — from cut to finished.
What to listen for: Measures and cuts square, deburrs the cut ends, cleans, primes where the pipe material, the cement's instructions and local code call for it, cements, seats the joint as the cement manufacturer directs — and then, the discriminator, gives the joint its cure time before any test.
Rushing cure is how a wall gets opened twice.
A candidate who narrates the order without prompting has done this on working jobs, not just watched it.
Sweat this copper joint.
What to listen for: Both surfaces cleaned, flux applied, even heat, solder drawn into the joint rather than dabbed over the top, wiped and left alone to set.
Then watch the finish: a plumber who tests the assembly with water or pressure before calling it done works the way you want your warranty to work.
Here's the rough-in drawing — mark the runs on this board where you'd pipe it.
What to listen for: Starts with the drawing: dimensions taken off the print rather than eyeballed, and the one genuinely ambiguous spot asked about out loud.
Print literacy separates the plumber who can run a job from the helper who has only watched one, and it is the skill your estimator and your inspector both depend on.
We've seeded one fault on this mock-up — find it.
What to listen for: The isolation sequence under a little pressure: what they rule out first, what check changes their mind, and whether they can say 'I need to open this to confirm' instead of pointing and guessing.
You are not watching for speed — you are watching for order.
Which answers are red flags?
None of these is automatically a no — but each should stop the interview long enough to verify, and a couple should end it.
- The licence nobody can check. They hold 'the licence' but cannot name the tier or who issued it (a state board, or a city or county where licensing is local). You verify a plumbing licence through the issuer's own record, so a candidate who cannot name the issuer cannot be verified before you offer.
- 'I don't need a licence for that.' Dodging the scope question — what they may run alone, what needs another licence's sign-off — is worse than holding a small licence. You are hiring for work that has to pass inspection.
- Guess-first diagnosis. Every story ends with 'so I replaced it and the problem went away' with no isolation step in between. You pay for the parts, the callback and the customer's patience.
- 'It drains now, that's fixed.' No camera, no why, no interest in the cause. Cabling is half the job; the half that stops the repeat call is finding out what caused the stoppage.
- The cure-time rusher. Proud of testing before joints have set — 'I've never had one let go.' Sooner or later the ceiling pays for it, during your warranty.
- Every past employer is a villain. One bad shop is a story; a row of them is a pattern. Ask what each owner would say, then call and compare.
- Side work on your truck. Talks casually about using your materials, your truck or your shop's name for jobs on the side. However good the hands, this is the behaviour your other techs will copy.
After the interview
Score the same day, on the same sheet.
Four rows — technical answers, customer answers, the practical task, credentials — each on a 1-to-5 scale, with a line of notes on the strongest and weakest answer.
Score before the next candidate sits down: memory grades on charm.
Ask every candidate the same questions in the same order.
That is what makes the scores comparable — and consistent questions and a written scoring sheet also give you a record of how each candidate was judged.
Under the Uniform Guidelines on Employee Selection Procedures, a hiring test that has adverse impact on a race, sex or ethnic group is treated as discriminatory unless it has been validated.
If you take candidates onto real work before you decide — a paid working interview — or you use a scored skills test, have an employment attorney review how you run it.
Weight the rows for your trucks.
A service-and-repair shop leans on the customer-explanation and diagnostic-sequence answers; a remodel or repipe crew leans on the bench tasks and the print.
Same sheet, different weights — just decide the weights before the first interview, not after the first offer.
Verify through the source before you offer.
Confirm the licence through the issuer's own record — the state board's public lookup for a state licence, or the city or county where licensing is local; our guide to verifying licences has the details — never a screenshot — and take the references by phone.
Federal rules set the order for the rest: after a conditional offer, you may ask disability-related questions and require medical exams, as long as you do it for all entering employees in that job category.
Before the offer, you may ask about current illegal drug use, but not about lawful prescription medication.
And if your background check comes from a screening company, the Fair Credit Reporting Act's notice and adverse-action steps apply.
Separately, the EEOC expects a targeted criminal-record screen that considers at least the nature of the offense, the time elapsed and the nature of the job.
When the sheet says yes, make sure the posting that found them still says the right things — and browse current plumber jobs to see what candidates see on the board.
This page is employer career information, not legal advice. Federal interview rules are enforced by the U.S. Equal Employment Opportunity Commission, and, for smaller employers (4 to 14 employees), national-origin and citizenship discrimination by the U.S. Department of Justice; state and local laws often add rules and reach smaller employers. Confirm what applies to your company with the agencies for your state and an employment attorney.
More hiring resources
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