Why your hot water runs out so fast
Hot water that runs out sooner than it used to can come from sediment in the tank, a failed heating element on an electric heater, or a household using more hot water than before. What you notice points to which, and flushing the tank, the first thing to try, costs nothing. Flushing once a year helps the tank last longer too, especially in areas with hard water.
Why the tank comes up short
Minerals in the water settle to the bottom of the tank over time. That sediment takes up space and insulates the water from the gas burner, or buries the lower element on an electric heater, so there's less hot water to go around. You'll often hear it, too: popping or rumbling when the heater runs.
Electric heaters have two heating elements, one near the top and one near the bottom. If the lower one fails, you get a short burst of hot water from the top of the tank and then lukewarm. That pattern points to the element, and flushing won't fix it.
Sometimes nothing's broken at all. A new family member, a bigger tub, or winter's colder incoming water can just ask more of the tank than it can deliver.
Possible causes
Minerals fill the bottom of the tank and reduce capacity.
On electric heaters, you get a short burst of hot water, then lukewarm.
Cold water mixes into the hot at the top of the tank.
A 40 gallon tank may not keep up with more showers or a big tub.
| What happens | Most likely | Fix |
|---|---|---|
| Hot at first, then lukewarm after a few minutes (electric) | Lower heating element failed | Replace the element. Flushing won't help. |
| Never gets very hot (electric) | Upper element or thermostat | Test or replace the part, or call a plumber. |
| Runs out fast, with popping or rumbling | Sediment in the tank | Flush it, then flush once a year. |
| Runs out faster only in winter | Colder incoming water | Normal. Turn the thermostat up slightly or stagger showers. |
| Lukewarm everywhere, even right after heating | Broken dip tube | A plumber can replace the dip tube. |
| Only one shower goes cool | The shower valve, not the heater | Adjust the anti-scald limit stop in that shower's handle. |
Flush the tank
- Check the thermostat settingMake sure it hasn't been bumped down. About 120°F is a common setting. On electric heaters, the dials are behind the access panels, so turn off the breaker before opening them.
- Turn off power or set gas to PILOTFor electric, switch off the breaker. For gas, set the control to PILOT or VACATION. If you can, give the water a few hours to cool so it's less likely to scald.
- Connect a hose to the Screw a garden hose onto the drain valve and run it to a floor drain, driveway or outside where hot water won't cause harm.
- Flush out the sedimentClose the cold supply, open a hot tap somewhere in the house, then open the drain valve. When the flow slows, briefly reopen the cold supply to stir up sediment, and repeat until the water runs clear.
- Refill before turning it onClose the drain, open the cold supply, and wait until water flows steadily from the hot tap before restoring power or gas.
- Turn it back on and checkTurn the breaker back on, or set the gas control from PILOT back to its usual setting. Give the tank an hour or two to heat, and check the drain valve for drips over the next day. If it drips, snug the valve closed or cap it.
Watch it done
- The flush water runs clear
- Hot water lasts longer once the tank has had an hour or two to heat
- No drips at the drain valve over the next day
Still lukewarm on an electric heater? A heating element has probably failed.
If it still runs out early
If the water is lukewarm on an electric heater, one heating element has probably failed. It's a common, inexpensive part, but replacing it involves wiring and draining the tank.
If there's more demand than the tank can handle, try staggering showers or installing low-flow showerheads.
If only one shower runs out quickly, take the handle off and look for a plastic anti-scald limit stop. Turning it a notch lets the valve reach hotter water. The heater may be fine.
What a pro typically charges (a rough estimate; prices vary by area): Tank flushing by a plumber runs $100–$250. An electric element replacement typically costs $200–$350.
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