Why is my water heater not making hot water?
The cause depends on the fuel. On a gas tank, the most common repair is a worn thermocouple, the sensor that tells the gas valve the pilot is lit, according to HomeGuide. A faulty gas control valve is the other usual suspect. On an electric tank, the most common repair is a failed heating element, followed by a bad thermostat or a tripped breaker.
Some problems apply to any tank. Sediment on the bottom slows heating, a broken dip tube lets cold water mix into the hot outlet, and a tank that is too small simply runs out.
- No hot water at all, gas: pilot out, thermocouple or gas control valve.
- No hot water at all, electric: tripped breaker, reset switch or failed upper element.
- Lukewarm or short supply: failed lower element, thermostat, sediment or dip tube.
- Water too hot: thermostat set too high or failing; CPSC recommends 120°F.
How do I relight a pilot or reset a water heater?
For a gas water heater with a standing pilot, follow the lighting instructions on the label on the tank. PG&E's advice when a pilot is out: shut off gas at the appliance's shutoff valve and wait five minutes for gas to clear before relighting. If you smell gas at any point, stop, leave the home and call 911, then PG&E at 1-800-743-5000. If the pilot keeps going out, the thermocouple or gas valve likely needs replacement.
Many electric water heaters have a reset button on the high-temperature cutoff behind an access panel. Switch off the breaker before removing the panel, because the wiring behind it is live. If the reset trips again, the thermostat or an element has likely failed, and pressing it repeatedly will not fix that.
How do I turn a water heater off and back on?
To turn a gas water heater off, turn the control knob to OFF; for a short absence, many models have a PILOT or VACATION setting. For an electric water heater, switch off its breaker. If the tank is leaking, also close the cold-water supply valve on the pipe that feeds the top of the tank.
To turn it back on, make sure the tank is full first: open a hot faucet and wait until water flows steadily without sputtering. Then relight the pilot following the label, or switch the breaker back on. Turning on an electric heater with an empty tank can burn out the elements.
How long does it take for a water heater to heat up?
It depends on the tank size and how fast the heater recovers. A storage water heater's first-hour rating, printed on its yellow EnergyGuide label, tells you how many gallons of hot water it can deliver in an hour starting from a full tank. A heat pump water heater heats more slowly in heat pump mode than with its backup electric elements, and DOE's building science guidance notes that cold incoming water and cool air in winter lengthen its recovery time.
Tankless units heat water as it flows, but each has a minimum flow, 0.4 to 0.9 gallons per minute according to a DOE Building America guide, before the burner fires. If a tank that used to recover quickly now takes much longer, sediment, a failing element or a burner problem is worth checking.
Is it worth repairing an old water heater?
If the tank is under about 10 years old and the problem is a part, repair is usually cheaper than a $600 to $3,100 replacement (HomeGuide, national). DOE says most tank water heaters last 10 to 15 years and suggests shopping for a replacement once yours is more than 7 years old. A leak from the tank body cannot be repaired; HomeGuide says leaking tanks typically require replacing the water heater.
Which water heater repairs are unsafe to do yourself?
Gas valves, burners, venting and gas line connections are not DIY work. A disconnected or blocked vent can push carbon monoxide into the home; the EPA lists back-drafting gas water heaters as a CO source. Water in a tank can also scald: CPSC says 140°F water causes third-degree burns in 6 seconds. HomeGuide notes that manufacturer warranties and local codes may require a licensed plumber for repairs, and any work that needs a permit requires a licensed contractor under CSLB rules.
| Repair | Fixr range | HomeGuide range | Typical symptom |
|---|---|---|---|
| Thermocouple | $150–$325 | $100–$325 | Gas pilot won't stay lit |
| Heating element | $200–$750 | $100–$350 | Electric tank runs out fast or stays lukewarm |
| Thermostat | $100–$250 | $100–$350 | Water too hot or not hot enough |
| Anode rod | $125–$300 | $150–$350 | Corrosion protection; HomeGuide says plumbers suggest replacing every 3–5 years |
| Temperature and pressure relief valve | $100–$250 | $50–$300 | Valve drips or won't seat |
| Dip tube | $100–$250 | $100–$350 | Hot water turns lukewarm quickly |
| Gas control valve | Not listed | $150–$550 | Gas tank won't light or heat |
| Tank flush | Not listed | $75–$250 | Rumbling, slow heating, sediment |
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Frequently asked questions
Why does my water heater pilot light keep going out?
Why is my hot water only lukewarm?
Can I repair my water heater myself?
Sources
- How much does water heater repair cost? (2025–2026) — HomeGuide
- How much does water heater installation or replacement cost? (2026) — HomeGuide
- Water Heater Repair Cost (updated Aug. 29, 2025) — Fixr
- Avoiding Tap Water Scalds (Document 5098) — U.S. Consumer Product Safety Commission
- Gas safety — PG&E
- Decision Guidance for Heat Pump Water Heaters, Level 3 (sizing worksheet, recovery, condensate) — U.S. Department of Energy, Building Science Education Solution Center
- Measure Guideline: Transitioning to a Tankless Water Heater (Building America, 2012) — U.S. Department of Energy / IBACOS
- Energy Saver Guide: Tips on Saving Money and Energy in Your Home (2022) — U.S. Department of Energy
- Energy Savers: Tips on Saving Money and Energy at Home — U.S. Department of Energy
- Carbon Monoxide's Impact on Indoor Air Quality — U.S. Environmental Protection Agency
- License Requirement for Minor Work Increases from $500 to $1,000 (CSLB #24-07, Dec. 31, 2024) — Contractors State License Board (CSLB)
- Water heater repair services: costs and FAQs (Los Angeles page, 2026) — HomeGuide