There's nothing worse than when you don't have hot water for your shower. The two main reasons for the lack of hot water boils down to either faulty heating elements or sediment buildup. Knowing how to check these issues will put you well on your way to having a piping hot shower.
The Heating Elements
Heating elements are electrical coils responsible for heating water in your water tank. These two parts work as a team to keep your water hot when you want it. When one of these elements goes out, you'll notice a reduction or complete absence of warm water. Depending on which element is having issues, it will determine what symptoms your water heater gives you.
Upper Element - The upper element is responsible for heating the water that is drawn first from your tank. It works in a rotation with the lower element. First, it heats the water in the upper part of your tank. Then the electrical current stops powering the top element and switches to the bottom. When the top element malfunctions, you won't have access to hot water.
Lower Element - Your lower element heats water held in reserve in the lower portion of your tank. Cold water flows in the bottom of the container to be warmed by the lower element. If this part goes out, you'll still have some hot water, but a reduced amount.
To check your heating elements, you'll need to use a multimeter. Turn off the breaker connected to your water heater to disable the power. Remove the cover to gain access to the element you want to test. Connect the multimeter to the screws associated with the element on the panel. If you get a low reading, such as 1Ω, your part is faulty. Consult your water heater's manual for an appropriate range for your heating elements.
When sediment builds up in your water tank, it will reduce the overall amount of hot water available. Your tank will still be capable of producing hot water - so you won't experience a total loss of warm water. However, the more sediment there is, the less hot water you'll have.
Now, both heating element issues and sediment buildup will present themselves with reduced hot water or none at all. However, sediment issues will present themselves with rust-colored water from the hot water tap. You may also hear a rumbling noise.
Once you've narrowed down the issue, reach out to a plumber. They will be able to either flush your hot water tank in the case of sediment issues or replace the broken heating elements. If either problem is severe, the plumber may have to replace your hot water tank.