Last updated: July 2026 · Reviewed against A.O. Smith and Rheem service documentation
Have a tankless unit? See tankless water heater repair instead. No hot water at all usually means a total failure: a gas water heater with its pilot out, or an electric one with a tripped breaker or failed heating element. Not enough hot water, or water that runs cold fast, points to a different set of causes — a broken dip tube, sediment, or a failing element. Here is how to diagnose both, by fuel type.
No Hot Water vs. Not Enough
These are different problems. No hot water at all means the heater is not heating — a power, pilot, or element failure. Some hot water that runs out fast means it is heating but not keeping up — usually sediment, a bad dip tube, or one of two elements failing. Identify which you have before troubleshooting.
Electric Water Heater: No Hot Water
- Tripped breaker: check the panel and reset the water heater breaker. If it re-trips, you likely have a shorted element.
- Tripped high-limit reset: behind the upper access panel is a red reset button on the thermostat. Press it. If it trips again, the thermostat or element is faulty.
- Failed heating element: electric heaters have two elements; if the upper one fails you get no hot water, if the lower fails you get a little then it runs cold. Elements are $15–$30 and testable with a multimeter.
Gas Water Heater: No Hot Water
On a gas unit, no hot water almost always means the burner is not firing. The usual culprit is the pilot light going out — see our full guide to the water heater pilot light. If the pilot is lit but the burner will not fire, suspect the thermostat/gas control valve. Check that the gas supply valve is open and other gas appliances work.
Running Out of Hot Water Fast
If you get hot water but it runs cold quickly, the causes are different: a broken dip tube (sends cold water to the top where it mixes with hot), heavy sediment buildup reducing capacity, a failed lower element (electric), or simply an undersized tank for your demand. Flushing the tank helps with sediment; a dip tube or element needs replacing.
When to Call a Pro
Call a professional if the breaker keeps tripping (shorted element or wiring), if a gas burner will not fire after confirming the pilot, or if you are not comfortable testing elements or working with gas. If the tank is also leaking, see why your water heater is leaking — a failing tank often accompanies heating problems in an old unit.
FAQ
Why do I suddenly have no hot water?
On gas units, a pilot light that went out is the most common sudden cause. On electric units, a tripped breaker or a tripped high-limit reset button. Check those first — both are quick to fix and account for most sudden no-hot-water calls.
Why is my water heater not heating water?
The heater is getting no heat input: no power/tripped breaker or a failed element on electric units, or an out pilot / unfired burner on gas units. A failed thermostat can also stop either type from heating.
Why does my hot water run out so fast?
Usually a broken dip tube, sediment reducing tank capacity, or a failed lower heating element on an electric unit. Flushing the tank helps with sediment; the dip tube or element needs replacing.
Sources: U.S. Department of Energy — Water Heating · manufacturer service documentation (A.O. Smith, Rheem, Bradford White).