Why Does My Hot Water Run Out So Quickly?

Hot water is created by a hot water cylinder that has a limited capacity. In general, this capacity is enough so that you never run out but if your hot water runs out from regular use it indicates a problem. Today, I will explain why hot water runs out so quickly.

Overall, it’s best to flush out the water tank before calling a plumber. It can run out quickly because there is a build-up of hard water deposits or sediment in the tank, the dip tube is broken, the temperature setting is too low, or one of the heating elements is broken.

hard water deposits or sediments coming out of a hot water tank
Image from 3D Air Services, LLC

The other potential issue is if multiple people take long showers around the same time. Below, I will explain how to identify each of these issues yourself if it’s possible so you can have consistent hot water that virtually never runs out.

Reasons Why Hot Water Runs Out Quickly and How To Tell

There are quite a few reasons why hot water runs out quickly. But, other than a few people in your household taking very long showers back to back, all of the causes are isolated to an issue with the hot water cylinder. This makes identifying and fixing the issue very simple. Here are the reasons why and how to identify if it’s what’s causing it.

Hard water deposits or sediment build up in the hot water cylinder

Some regions have hard water. If you live somewhere that has hard water you will know about it because it will cause discoloration in the toilet bowl. Hard water deposits accumulate slowly over time but they will fill up a hot water cylinder and reduce the capacity. 

Some water also contains minor amounts of sediment. This sediment can also fill up slowly over time. To see if this is what is causing it, flush your hot water cylinder. How to do that is explained in the video below:

Temperature is set too low on the hot water cylinder

The temperature on a hot water cylinder can be adjusted. If it was accidentally set too low, the water will take longer to heat up. The temperature can be adjusted using a screwdriver. The temperature dial is located behind a panel that is held in place by a few screws.

The dial has written on it what different temperatures, and you can turn the dial to adjust it. The temperature should be set below 158°F (70°C) because anything hotter than this is hot enough to cause a burn. Ideally, it should be set to 140°F (60°C). Anything higher than this will cause increased power consumption which isn’t required.

One of the heating elements has failed

a person holding one of the heating elements of a hot water cylinder
Image from JMD Plumbing and Heating

Most electric hot water cylinders have two heating elements. If only one is working it will provide hot water, but it will run out quickly. If this is the issue it requires a plumber or electrician to identify it. Therefore, you should try the other steps on this list before doing this step.

The dip tube is broken and needs to be replaced

A dip tube is a tube that goes from the top of a hot water cylinder to the bottom. It’s where cold water enters a hot water cylinder. If the dip tube is cracked or broken cold water can enter the hot water cylinder at a different location, and not at the bottom of the tank. 

a person holding new and broken hot water cylinder dip tube
Image from Foemmel Fine Homes, Corp.

This causes the hot water to mix with water that is already heated and can create lukewarm water. Or, the water can be hot and then cold. This requires a plumber to replace, therefore, it’s best to save this step until last, and identify if it’s one of the other reasons on this list first.

The shower head is a high-flow shower head

This is more likely to be the issue if you’ve just moved into a house and the hot water runs out quickly. A high-flow shower head will feel like a massage on your back when the water comes out. Whereas, a low flow shower head will provide just enough water to be useable and no more. If the water pressure feels strong then it means you have a high-flow shower head. 

a high-flow shower head
Image from Best Deals – US

You will need to either install a new shower head, take shorter showers, adjust the water pressure on the shower handle (where possible) so it’s not turned up to the max, or get a larger water tank.

How Long Should Hot Water Last in a Home

Hot water will run out if a hot water tank is empty before new water that enters can be heated. There are a few different sizes of hot water cylinders that can be installed in a home. But, here’s how long hot water should last in a home.

As a general rule, hot water should never run out. Provided it’s the right size for the number of people who live in a home. A small tank which is 50 to 60 gallons (227 to 272 liters), is enough for 2 to 4 people. Whereas, an 80-gallon (363-liter) tank is good for 5 or more people. 

According to Bob Villa, for each additional person using an 80-gallon tank (ideal for 5 people), you get a hot water tank that is 10 gallons bigger.

white-colored hot water cylinders with different sizes
Image from Vaillant UK

But, if people take long showers, back-to-back showers, or use a lot of hot water such as running a bath, taking a shower, using a dishwasher, and a hot laundry cycle at the same time the hot water can run out.

There are also different-sized hot water cylinders. The size of a hot water cylinder is matched to the number of people in a home. 

It’s also important to be a little bit aware of how much hot water is getting used. For example, if everyone in your household has a shower in the morning and your hot water runs out, it’s generally worthwhile getting a larger hot water tank.

Why Hot Water Will Run Out After One Shower

Virtually all hot water tanks are large enough so that they won’t run out after one shower, provided you don’t tank a shower that is longer than about 30 minutes. If your hot water is running out after only one shower, here’s what causes it to happen, and what you should do.

As a general rule, there is a problem with your hot water tank. Various parts of a hot water tank can fail, such as the dip tube or the heating elements. How to troubleshoot this happening is explained below.

I have covered the 5 issues with a hot water tank that will cause it to run out quickly near the top of this article. Some can be identified and fixed yourself, whereas others will require a plumber. 

But, it’s worth pointing out that if a few people have taken a shower before you, they may have used up all the hot water. Especially, if the hot water tank is on the smaller side.

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