No Hot Water? What to Check First

When there’s no hot water, A. O. Smith, a water heater maker, says the most common causes are a tripped breaker on an electric heater and a pilot that has gone out on a gas one: “These are the simplest and most common causes of no hot water.” Other causes it lists include a failed part (a heating element or thermostat on electric models; the gas supply or gas control on gas models) and a tank that’s run out or is too small for the household. Don’t relight the pilot, turn gas valves or reset anything on the heater yourself; tell a licensed plumber what you see. The checks below are the ones that are safe to make. If you smell gas, leave the house and call your gas utility or 911 from outside.

First: a few safe checks

• Is it every faucet, or just one? If only one shower runs cold, Fixr says the issue “may not be connected to your water heater” and may be that shower’s mixing valve.
• Has someone just used a lot of hot water? A tank needs time to reheat. A. O. Smith says “gas tanks need 30-40 minutes, electric tanks need 60-90 minutes.”
• Is there water around the heater? Portland’s water bureau lists “check your tank for leaks” first under “Water not hot.” If there is, see water heater leaking from the bottom. Keep away from water near the heater’s electrical parts.
• Do you know the heater’s age? It matters for the repair-or-replace decision below.

Electric water heater: likely causes

A. O. Smith calls a tripped circuit breaker “a very common reason for an electric water heater not working,” and links it to possible “electrical shorts, loose wires, and grounded heating elements.” Its electric heater manual lists three causes of no hot water: no power to the heater, an open “High Temperature Limit Switch,” and a “non-functioning upper thermostat.” The high-limit switch shuts the heater off when the water gets abnormally hot.

If the breaker for an electric water heater has tripped, or the heater’s high-limit switch has shut it off, that’s a job for a licensed plumber or electrician. It shut off for a reason. Don’t press the reset button. The manual says that because the high limit “operates only when abnormally high water temperatures are present,” a “qualified service agent” should be contacted “to determine the reason for operation before resetting.”

Don’t open the heater’s panels either. A. O. Smith warns: “High-voltage electricity can kill, and water heater components remain live even when the unit isn’t actively heating.” CPSC notes that reaching the thermostats means removing the heater’s upper and lower access panels. Testing and replacing elements and thermostats is plumber’s or electrician’s work.

Gas water heater: likely causes

Many gas tank heaters have a small pilot flame that lights the burner. A thermocouple watches that flame; Fixr says it works “by monitoring the heat of the pilot light and then allowing gas to flow through to the burner.” For tank heaters, A. O. Smith lists gas supply problems, which can stop the burner from lighting “and can also cause the pilot to extinguish,” and blocked air screens that restrict combustion air. It also lists a faulty gas control valve, which it says “should be inspected and replaced by a professional if found to be defective.”

Relighting a pilot means working with the gas control, so leave it to a licensed plumber. The same goes for a pilot that won’t stay lit or a burner that won’t fire.

If you smell gas: don’t light anything, don’t switch lights on or off, and don’t make calls from inside. A. O. Smith’s manual says “Do not try to light any appliance” and “do not use any phone in your building.” Leave the house and call your gas utility or 911 from outside. Washington’s utility regulator says to call “from a safe distance away from the odor” and to wait until utility crews or first responders say it’s safe to go back in.

When the water is only lukewarm

Warm-but-not-hot water has its own list. A. O. Smith’s manual names thermostats “set too low,” a failed lower element on electric models, “sediment or lime in tank,” and a “heater too small for job.” Another is a broken dip tube, the plastic pipe that carries cold water to the bottom of the tank. Fixr says “when dip tubes break, the hot water runs out very quickly.” Portland’s water bureau links white plastic particles in the water to a dip tube “breaking down inside the tank.”

A. O. Smith also notes that newer heaters “are now factory preset at a lower temperature and inlet tubes have been shortened,” and that both affect how much hot water a heater can supply. Before anyone turns the temperature up, keep scalding in mind. CPSC “urges all users to lower their water heaters to 120 degrees Fahrenheit,” and Portland says 115 to 120 degrees “can reduce the risk of scalding.” A plumber can check the setting and tell you whether the heater is simply too small.

When to call a plumber

• You smell gas: leave first, then call your gas utility or 911 from outside.
• The heater’s breaker has tripped, or the heater has shut itself off.
• The pilot won’t light or stay lit, or the burner won’t fire.
• There’s water around the heater, rusty hot water, or loud rumbling.
• The water never gets past lukewarm, or the hot water runs out much faster than it used to.

Repair or replace the heater?

The common repairs cost far less than a new heater. Prices from two guides, each for the work named:

This Old House says to “consider replacement when your unit reaches 10 years old,” and that “when repair costs exceed half the price of a new unit, replacement becomes the more economical choice.” To weigh your own numbers, try our repair-or-replace calculator, or read how long water heaters last.

Sources

• A. O. Smith — Is Your Hot Water Not Getting Hot? Common Causes & What To Do About Them (manufacturer guide, undated; accessed Oct 31, 2026)
• A. O. Smith — Residential Electric Water Heaters Instruction Manual, Part No. 185762-002 (2012), p. 14 (high limit) and p. 20 (Troubleshooting Guidelines)
• A. O. Smith — Direct Vent Residential Gas Water Heater, Installation Instructions and Use & Care Guide (2013), p. 1 (What to do if you smell gas)
• A. O. Smith — Technical Bulletin #36: Not Enough Hot Water – Electric (undated; accessed Oct 31, 2026)
• Washington Utilities and Transportation Commission — Pipeline Emergencies (undated; accessed Oct 31, 2026)
• City of Portland, Water Bureau — Maintaining your water heater (undated; accessed Oct 31, 2026)
• U.S. Consumer Product Safety Commission — Avoiding Tap Water Scalds, Publication 5098 (print date code 03/2012)
• Fixr — Water Heater Repair Cost (updated Aug 29, 2025)
• Fixr — How Much Does It Cost to Install a Water Heater? (updated Jan 27, 2026)
• This Old House — How Much Does Water Heater Installation Cost? (updated Jun 17, 2026; cost data from The Home Depot and market research)

Checked 2026-10-31