Wondering what's going on in there?
How your water heater works, in plain English
A tank water heater works like a big kettle that's always on. It keeps a tank of water hot, so it's ready when you turn on a tap.
- Cold water comes in. It flows in at the top and down a plastic tube to the bottom of the tank. Pros call it the dip tube.
- Heat warms the water. Gas heaters use a burner under the tank, lit by a tiny pilot light or an electronic igniter. Electric heaters use one or two heating elements, metal rods inside the tank.
- A thermostat watches the temperature. On gas heaters, it's the knob on the front. On electric heaters, it's hidden behind the side panels. When the water cools, it turns the heat back on.
- Hot water goes out. Hot water rises, so it leaves from the top of the tank and travels to your taps.
So no hot water comes from one of a few things:
- The tank ran out and is still reheating.
- The heat is off: a pilot light that's out, a tripped breaker or reset button, or a knob turned down.
- A part that makes the heat failed: the gas control, a heating element or a thermostat.
- The tank heats poorly: sediment on the bottom, or a broken dip tube mixing in cold water.
If only one faucet is cold, the water heater is usually fine. The problem is in that faucet. This guide covers tank water heaters, gas and electric.
Hot water smells like rotten eggs? See our guide to water that smells like rotten eggs.
Rather not do it yourself? Call a plumber.
That's a fine choice. Maybe you're busy. Maybe you're selling the house and just want it done right. A plumber can find the part that quit and get your hot water back.
Most plumbers charge $45–$200 an hour, and some add a fee to come out.
Find water heater repair near you
Find water heater repair near me →Opens Google Maps. We don't ask for your number.
What to say
Calling a pro? Here's what to say.
A few lines to read when they pick up, and the questions to ask before anyone comes out.
Before you call
Say this
Hi. My water heater isn't making hot water. When's the soonest you can get here? And what's your fee for the visit? Does it go toward the repair?
Always ask
- What's your fee to come out, and does it go toward the repair?
- Do you charge by the job or by the hour?
- Will you tell me the full price before you start any work?
Watch out if
- They push a full replacement on the first visit for a small problem.
- They won't give you a price before starting.
- They add an emergency fee without telling you first.
Feeling pushed to decide on the spot? You can say no and hang up. You owe nothing for a phone call.
Answer up to 5 quick questions. We'll give you the words a pro uses.
Answer the questions →More of a list person?
Common symptoms, causes, tests and costs
Find the row that sounds like yours. The quick test is something you can check yourself in a few minutes.
| What you notice | What it probably is | Quick test | Do it yourself | With a pro | Verdict |
|---|---|---|---|---|---|
| Hot water ran out after heavy use | Nothing's wrong. It's refilling | Wait an hour, then try a hot tap | Free | Not needed | FIXSee the answer: Nothing's wrong. It's refilling |
| Only one faucet or shower has no hot water | That faucet's mixing part | Try the hot water at a different faucet | Pro job | $200–$400 | CALLSee the answer: That faucet's mixing part |
| Can't find or safely reach the water heater, or you rent | Let a pro (or your landlord) take it from here | None. Hand it off | Pro job | $50–$150 | CALLSee the answer: Let a pro (or your landlord) take it from here |
| A box on the wall with no tank, and no hot water | Tankless heaters need their own checks | Look for an error code on its screen | Pro job | $228–$1,017 | CALLSee the answer: Tankless heaters need their own checks |
| Knob on Vacation, Pilot or Off, or turned way down | The knob is set too low | Look at the knob on the front of the tank | Free | Not needed | FIXSee the answer: The knob is set too low |
| Water heater breaker was tripped | The breaker tripped | Look at the breaker marked water heater | Free | Not needed | FIXSee the answer: The breaker tripped |
| Electric heater, breaker on, red reset button had tripped | The overheat reset button tripped | With the breaker off, press the red button behind the upper panel | Free | Not needed | FIXSee the answer: The overheat reset button tripped |
| Gas heater; the small pilot flame is out | The pilot light went out | Look through the window for the tiny blue pilot flame | Free | Not needed | FIXSee the answer: The pilot light went out |
| Pilot is out, and the gas stove won't light either | Gas isn't reaching the water heater | Does your gas stove light? | Pro job | $50–$150 | CALLSee the answer: Gas isn't reaching the water heater |
| Pilot is out and there's no label, or it keeps going out | The pilot light is out | Look for the tiny blue pilot flame and a relighting label | Pro job | $150–$325 | CALLSee the answer: The pilot light is out |
| Pilot stays lit for hours or days, then goes out again | Air or venting is putting the pilot out | Notice how long the pilot stays lit before it goes out | Pro job | $50–$150 | CALLSee the answer: Air or venting is putting the pilot out |
| Pilot lit but the burner never comes on, or a blinking status light | The gas control or its sensor failed | Run a hot tap and watch for the big burner to light | Pro job | $150–$350 | CALLSee the answer: The gas control or its sensor failed |
| Electric heater, breaker on, no heat or only lukewarm water | A heating element or thermostat failed | Breaker on, reset button not tripped, still no heat | Pro job | $100–$750 | CALLSee the answer: A heating element or thermostat failed |
| Water heater breaker trips again after one reset | Something is shorting out | Reset the breaker once; does it trip again? | Pro job | $200–$750 | CALLSee the answer: Something is shorting out |
| Lukewarm, runs out fast; rumbling or popping from the tank | Built-up sediment in the tank | Listen to the tank while it heats | Pro job | $100–$250 | CALLSee the answer: Built-up sediment in the tank |
| Hot water turns lukewarm fast; bits of white plastic in faucet screens | A broken cold-water tube inside the tank | Check faucet screens for small bits of white plastic | Pro job | $100–$250 | CALLSee the answer: A broken cold-water tube inside the tank |
| Rotten-egg or gas smell near the water heater | You may have a gas leak | None. Leave the house | Pro job | $50–$150 | CALLSee the answer: You may have a gas leak |
2026 U.S. averages, rounded. Pro prices include parts and labor. Most plumbers charge $45–$200 an hour, and some add a fee to come out. Nights, weekends and big cities cost more. See all repair prices
Want proof it's working?
The hot tap test
This tells you whether your water heater is really heating. You need a few minutes and, if you have one, a kitchen thermometer.
- Don't use any hot water for an hour.
- Turn on the hot water at the kitchen sink and let it run for 2 minutes.
- It should feel clearly hot, too hot to keep your hand under for long.
- Hold a kitchen thermometer in the stream for 30 seconds. Most homes keep it around 120 degrees, which is hot but not scalding.
- Keep the tap running. A full tank should stay hot for a long shower's worth of water.
- Hot, and it lasts: it's working.
- Hot at first, then lukewarm fast: sediment or a broken dip tube. Take the questions at the top.
- Never hot: the heat isn't coming on. Take the questions at the top.
Not sure it's safe to keep running?
Turn it off right away if…
- You smell gas or rotten eggs. Don't touch the water heater. Leave the house and call the gas company from outside.
- Your carbon monoxide alarm goes off. Get everyone outside and call 911.
- Water is pooling under the tank or dripping from the tank itself. A leaking tank can't be fixed.
- The relief valve on the side keeps spraying or dripping hot water.
- You smell burning, or see scorch marks near the electric panels.
- The breaker trips again after one reset.
To turn off a gas heater, set the knob to Off or Pilot. For an electric heater, turn off its breaker. If the tank is leaking, also close the cold water valve on the pipe above the tank.
Got a big repair quote?
Should you repair it or replace it?
Most water heater repairs cost a few hundred dollars. HomeAdvisor puts the typical repair at $228–$1,017, and a new water heater at about $875–$1,800, installed. Ask yourself three things:
- How old is it? Tank water heaters last about 8–15 years. The date is on the sticker on the side of the tank.
- Is the tank leaking? A leak from the tank itself means it's time for a new one. No repair fixes a rusted-through tank.
- The half rule. If the repair costs more than half the price of a new heater, get a replacement quote too.
Example: a $150 thermocouple on a 6-year-old heater is worth doing. A $350 gas control on a 13-year-old heater is worth comparing with a new one.
Ran into a word you don't know?
Water heater words, explained
Tap through these before you go looking. The drawings show roughly what each part looks like.
- Water heater
- The tall metal tank, usually in a garage, basement or closet, that keeps water hot for your taps.
- Gas knob
- The knob near the bottom of a gas water heater. It sets the temperature and has Pilot and Off settings.
- Gas control valve
- The box the knob is on. It opens the gas to the burner when the water needs heating.
- Pilot light
- A tiny blue flame that burns all the time and lights the main burner.
- Thermocouple
- A small metal rod next to the pilot light. It senses the flame and shuts off the gas if the flame goes out.
- Vent (flue)
- The cone-shaped hood and pipe on top of a gas water heater. It carries the fumes outside.
- Carbon monoxide alarm
- An alarm that sounds when it senses carbon monoxide, a gas you can't see or smell.
- Status light
- On some newer gas heaters, a small light that blinks a pattern to show what's wrong.
- Gas shutoff
- A handle on the gas pipe going into the water heater. In line with the pipe means open. Crossways means closed.
- Breaker
- A safety switch in your home's breaker box (the gray metal panel). Electric water heaters have their own.
- Reset button
- A red button behind the upper panel of an electric water heater. It cuts the power if the water gets too hot.
- Heating element
- A metal rod inside an electric water heater's tank that heats the water, like the coil in a kettle.
- Thermostat
- The part that turns the heat on and off. On electric heaters, it's behind each side panel.
- Dip tube
- A plastic tube inside the tank that carries cold water to the bottom.
- Sediment
- Minerals from your water that settle at the bottom of the tank over time.
- Relief valve
- A safety valve on the side or top of the tank that lets out water if the pressure or heat gets too high.
- Cartridge
- The part inside a faucet or shower handle that mixes hot and cold water.
- Tankless water heater
- A box on the wall that heats water only as it flows through. It has no tank.
Still have questions?
Questions people ask most
How long does it take for a water heater to make hot water again?
A water heater usually takes about an hour to heat a full tank again. Electric heaters often take longer than gas ones. If it's still cold after a couple of hours, something's wrong.
Is no hot water an emergency?
No hot water is usually not an emergency, but a gas smell or a carbon monoxide alarm is. For gas, leave the house now and call the gas company from outside. For a carbon monoxide alarm, get everyone out and call 911. Water pooling under the tank, or a relief valve that keeps spraying, means shutting the heater off and calling a plumber today.
Why is there no hot water in just one faucet?
When just one faucet has no hot water, the water heater is fine. The part inside that faucet or shower that mixes hot and cold has probably worn out or clogged. A plumber can usually replace just that part.
How do I reset my electric water heater?
To reset an electric water heater, turn its breaker OFF first. Take off the upper panel on the side of the tank, press the red button, and put the panel back. Turn the breaker ON and wait an hour. If it trips again, call a pro.
Can I relight my water heater's pilot light myself?
You can relight a water heater's pilot light yourself only if the label on the tank has clear relighting steps. Follow them exactly. If there's no label, or the pilot keeps going out, call a pro. If you smell gas, don't light anything. Leave and call the gas company from outside. If it goes out again, see "Why won't my water heater pilot light stay lit?" below.
Why won't my water heater pilot light stay lit?
A water heater pilot that goes out when you let go of the knob usually has a worn or loose thermocouple, the small rod that senses the flame. One that stays lit, then goes out every few hours or days, points to an air, vent or gas pressure problem, Bradford White says. If it still goes out with a new thermocouple, a safety switch may be the cause. Newer heaters have one that shuts the pilot off when it senses fumes or a blocked air supply. All of these are jobs for a pro.
Can I replace the thermocouple on my water heater myself?
We suggest a pro replace a water heater's thermocouple unless you've worked on gas appliances before. It means turning off the gas and working at the gas control. A pro usually charges about $150–$325 (Fixr; HomeAdvisor and Angi about $150).
Why is my water heater making popping or rumbling noises?
Popping or rumbling from a water heater usually means sediment. Minerals settle at the bottom of the tank, and water trapped under them pops as it heats. A plumber can flush the tank. On an old tank, ask whether it's worth it.
How long do water heaters last?
Tank water heaters usually last about 8–15 years. Tankless ones can last around 20. The date it was made is on the sticker on the side.
What if I have a tankless water heater?
With a tankless water heater, check its breaker, and its gas if it's a gas model. Then look for an error code on its screen. Write it down and call a pro who services your brand.
Who do I call when my water heater has no hot water?
Call a plumber or a water heater company for a water heater that won't heat. Call the gas company if you smell gas or none of your gas appliances work. For a tankless heater, look for a pro who services your brand.
How much does it cost to fix a water heater with no hot water?
Fixing a water heater with no hot water often costs nothing, if it's the knob, the breaker, the reset button or the pilot light. A thermocouple runs about $150–$325. A heating element runs about $200–$750. A new water heater runs about $875–$1,800.
How we built this
The questions follow the order a plumber checks a no-hot-water call: one tap or all of them, gas or electric, the temperature setting, then the pilot and burner (gas) or the breaker and reset button (electric). Each answer makes some causes more likely and others less likely.
Prices are 2026 national averages from published repair-cost guides, rounded. Your local prices will differ.
- HomeAdvisor, water heater repair cost (June 2026)
- Angi, water heater repair cost (read October 2026)
- Fixr, water heater repair cost (August 2025)
- This Old House, shower cartridge replacement cost (December 2025)
- Sears Home Services, why an electric water heater stops working (January 2026)
- A. O. Smith, no hot water help (read October 2026)
- Bradford White, troubleshooting guide and instructions for service, manual 238-51542-00A (April 2015)
- Fix.com, water heater pilot won't stay lit (read October 2026)
- U.S. Consumer Product Safety Commission, carbon monoxide questions and answers (read October 2026)
- ConsumerAffairs, cost to repair a water heater (September 2026)
How we make money: some links go to parts stores that pay us a small commission, and some pro listings pay us when you call them. Verdicts come from the diagnosis, not from who pays more.