Call a licensed plumber when the problem is behind a wall, floor or ceiling; on the water main, the main drain or the sewer line; on any gas line; on a water heater's gas, electrical or relief-valve side; when you cannot shut the water off at the fixture; or when several drains misbehave at once. Jobs at a single fixture you can isolate with its own shutoff, such as an aerator, a toilet flapper, a sink trap or a faucet cartridge, are reasonable DIY. The dividing line is not skill. It is whether you can stop the water and see the whole part.
This is the page the rest of our plumbing guides point to when they say "stop here". It sorts problems by symptom, says what each usually means, and says what to do while you wait.
The two-question test
Before any plumbing job, ask two things.
Can I isolate it? A fixture with its own shutoff, the stop under a sink or behind a toilet, can be worked on with the water off. If the only way to stop the water is the main shutoff, or the fixture's stop will not close, the job has already moved past the fixture.
Can I see all of it? A trap under a sink, a flapper in a tank and an aerator on a spout are in plain view. A pipe inside a wall, under a slab or buried in the yard is not, and neither is the cause of a problem that shows up in more than one room.
Two yeses: a reasonable DIY job, following the maker's instructions. Either no: call a licensed plumber.
When to call a plumber, by symptom
| Symptom | What it usually means | Call a plumber? | While you wait |
|---|---|---|---|
| Water spraying or pouring from a pipe | Supply pipe failure under pressure | Now | Close the main shutoff; keep clear of water near outlets and appliances |
| Ceiling stain, damp wall, warped floor | A hidden leak | Yes, soon | Photograph it and note whether it grows |
| Several slow drains, gurgling, or water rising in another fixture | Main drain or sewer blockage, or venting | Yes | Stop running water and flushing |
| Sewage backing up into a tub, shower or floor drain | Main line blockage | Now | Stop all water use; keep people and pets away |
| No water anywhere | Utility problem, main valve, or a frozen pipe | Check with the utility first | Ask the neighbors; check the main valve is open |
| Low pressure at every fixture | Main valve, pressure regulator, supply pipe or leak | Yes | Watch the meter with everything off |
| Water heater leaking, or its relief valve discharging | Tank failure, or a temperature or pressure problem | Yes | Keep clear of the discharge; never cap or plug it |
| A shutoff valve that will not close or leaks at the stem | A valve you cannot rely on in an emergency | Yes | Know where the main shutoff is |
| Moving a sink, adding a fixture, new pipe runs | New plumbing, often permit work | Yes | Ask your local building department about permits |
| A gas smell anywhere | A possible gas leak | Leave first, then call | See the gas section below |
Active leaks: the main shutoff comes first
Every household should know where its main water shutoff is before it is needed. It is often where the supply pipe enters the house, in a basement, crawlspace, garage or utility area, and some homes also have a valve at the meter that belongs to the water utility.
When water is escaping:
- Close the main shutoff.
- Keep away from water near electricity. If water is reaching outlets, appliances or the electrical panel, do not walk through it to reach anything electrical. If you can reach the breaker panel from dry ground, switch off the circuits for the wet area. If you cannot, stay out and call your electric utility or a licensed electrician.
- Call a licensed plumber, and photograph the damage before you clean up, for your insurer.
Slow, hidden leaks matter too, because they add up. The EPA's Fix a Leak Week page, updated March 2026 and read on 2026-09-11, states that the average household's leaks can account for more than 9,300 gallons of water wasted every year, and that nine percent of homes have leaks that waste 50 gallons or more per day. A simple check: turn off every tap and water-using appliance and watch the water meter. If it moves, water is going somewhere you cannot see, and that is plumber work.
Drains: one slow sink is yours, several are not
A sewage smell at one sink is usually a dry trap you can refill yourself, which our guide to a kitchen sink that smells like sewage walks through; a smell that returns after the trap is refilled points to venting, which runs behind walls. If the sink and the dishwasher back up together, the guide to a dishwasher that isn't draining shows how to tell whether the machine or the shared drain is at fault. A disposal that has gone sluggish or sour is usually its own cleaning job, covered in the full fix for a smelly garbage disposal.
Once two or more drains are slow, or running one fixture pushes water up in another, the blockage is in the main drain or sewer line. That needs a plumber with a camera and powered equipment.
If you have already poured a chemical drain cleaner into a drain that will not clear, tell the plumber what it was before they open anything. Poison Control's guidance on caustic household products, read on 2026-09-11, warns that chemical burns occur instantly if these products touch your mouth, eyes, or skin.
Gas is never a DIY plumbing job
Gas piping, gas connections to a water heater, range or dryer, and gas valves are not homeowner work at any size. Who may legally work on gas piping, and what needs a permit, varies by state and municipality. Your gas utility and your local building department can tell you what applies where you live.
Any home with gas appliances also needs working carbon monoxide alarms. CPSC's Carbon Monoxide Information Center, read on 2026-09-11, advises installing battery-operated CO alarms, or alarms with battery backup, on every level of the home and outside sleeping areas, and says that if you suspect CO poisoning, get outside to fresh air immediately, and then call 911.
If you smell gas, do not investigate it. The American Gas Association's guidance on using natural gas safely, read on 2026-09-11, is to leave the building immediately and take others with you; not to light a match or smoke, turn appliances or lights on or off, use a flashlight, start a car, or use a telephone; and to find a phone away from the area and call 911 or your natural gas utility.
Water heaters: the owner's list is short
A water heater combines scalding water, a pressure vessel, and either a gas burner or high-voltage electrical elements. Your heater's manual lists what the owner may do. Anything touching the gas supply, the electrical supply, the burner or the temperature and pressure relief valve belongs to a licensed plumber, or on a gas unit to whoever is licensed for gas work in your area.
The temperature setting is the part people ask about most. The CPSC safety alert Avoiding Tap Water Scalds, read on 2026-09-11, urges all users to lower their water heaters to 120 degrees Fahrenheit, and states that most adults will suffer third-degree burns if exposed to 150 degree water for two seconds, with burns also occurring at six seconds of 140 degree water or thirty seconds of 130 degree water. For gas water heaters, the same alert says to call your local gas company for instructions, because thermostats differ.
The relief valve is a safety device. A valve that drips or discharges is telling you something is wrong with temperature or pressure. It is never plugged, capped or removed, and a heater whose valve is discharging needs a licensed plumber.
When an older heater starts failing, the repair-or-replace question follows the same logic we apply to other big household machines in our appliance repair-or-replace triage guide: the age of the unit, the cost and likelihood of the next repair, and what a replacement would actually solve.
Permits and licenses: it depends where you live
There is no single national rule here. Plumbing licenses are issued by states and sometimes by cities, and which jobs need a permit is set locally. Only your local building department can tell you what applies to your address.
When you hire:
- Ask for the license number and check it with the licensing board in your state or city.
- Ask whether the job needs a permit, and who will pull it.
- Get the scope in writing, including what happens if they open a wall and find more.
What to write down before the plumber arrives
This shortens the visit and makes a quote more precise, and it is something every homeowner can do well.
- Which fixtures are affected, and whether it is hot, cold or both.
- When it started, and what happened just before: utility work on the street, a freeze, a new appliance, a recent repair.
- The meter check, if you did one, and whether the dial moved.
- Photos of the leak, stain, valve or backed-up drain.
- The rating plate on the water heater, with brand, model and serial number, if the heater is involved.
- Anything poured down the drain, by product name.
What stays a DIY job
Fixture-side jobs with the fixture's own stop closed are reasonable for a careful homeowner: cleaning a faucet aerator, replacing a toilet flapper, clearing a sink trap by hand, refilling a dry trap, and cleaning the dishwasher filter that catches food before it reaches the drain. Each stops at the same point: if the stop will not close, or the part connects to something inside the wall, you have reached the plumber's side of the line.
FAQ
Should I call a plumber or the water utility when there is no water? Check with the neighbors and the utility first. If the street has water and you do not, and your main valve is open, call a licensed plumber.
What should I do if I smell gas near the water heater? Leave the building with everyone in it, without switching anything on or off, and call 911 or your gas utility from a phone away from the area, following the American Gas Association's guidance. Repairs come after, from someone licensed for gas work where you live.
Do I need a permit for plumbing work? It depends on the job and your jurisdiction. New pipe runs and relocating fixtures commonly need one. Your local building department is the only reliable answer for your address.
The short version
If you can shut the water off at the fixture and see the whole part, it is probably yours. If the problem is behind a surface, on the main, the sewer or a gas line, involves the water heater's safety systems, or shows up in more than one room, call a licensed plumber, and use the time before they arrive to write down what you have seen.
