If you have a steady supply of hot water but it runs out very quickly, there are a few different reasons this could be happening. The good news is that most fixes don't require replacing your entire water heater, and since your water heater doesn't have many parts, narrowing down the problem is a quick process.
Pilot Light Not On
The pilot light on gas water heaters keeps the bottom burner running when it's necessary to heat water, and if the pilot light has gone out, the burners won't ignite. This can cause you to have short access to hot water, but only for minutes at a time as the heater pulls all the hot water from the surface.
This is typically the easiest problem to fix. Check out the lower part of your water heater; there's usually a panel that opens up to reveal the pilot light, and from there, you can see if it's on or not. If not, follow the instructions printed on your water heater to light the pilot light again. It's possible it simply went out due to a draft or lack of combustible air. If it won't light, you may need to get your thermocouple replaced, but this is a small part and inexpensive to take care of.
Broken or Missing Dip Tube
The dip tube is attached to the cold water inlet pipe on the top of your water heater, and it pushes all the cold water to the bottom of the tank where it can be heated. Over time, these tubes can break or fall off, meaning that instead of the cold water going all the way to the bottom of the tank, it will remain on the surface, which is where your hot water is pulled from.
Replacing a dip tube is best left to a plumber or water heater technician, but don't worry; the process is relatively simple, and parts are inexpensive.
Bad Lower Heating Element
The lower heating element is the part of electric water heaters that heats all the cold water that's pushed to the bottom. If there's a problem with this element, the cold water at the bottom will not heat. Some water at the top will still be heated by the upper heating element, but since this only keeps the top warm for the purpose of consistency, you will run out of hot water quickly.
If everything else seems to be working correctly but you're still having issues, have a technician inspect this element to see if it needs replacing. To be extra thorough, you can first check your circuit panel to make sure there are no broken circuits and that your heater is receiving power.
Buildup of Sediment
Tiny particles of sediment exist in your water, and though much of this is filtered out, it can slowly build up over time. This poses two main problems: first, it reduces the effectiveness of your bottom burner, and second, it reduces the total capacity of your heater.
The solution to this is to flush your water heater. After you shut off your supply of electricity or gas, drain all the water from the tank and let it refill. This will let out much of the sediment, but in order to be truly effective, your water heater should be flushed about once a year.
For additional information, contact a company like Marcum Plumbing Services, Inc.