5 Reasons a Water Heater Doesn't Make Enough Hot Water

Hot water faucetImage source: Pixabay

A problem with "not enough hot water" is the most common complaint, whether you have a new or old water heater, gas or electric model, tankless or a tank-type equipped with the storage tanks of 30, 40, 50, or more gallons. This water heater issue followed by lukewarm water and hot water that runs out fast can occur suddenly and with no warning signs.

Homeowners often complain that water is not hot enough at the point of use, such as a shower, dishwasher, bathtub, also upstairs, in the morning or evening, and whatever situation they have.

When a water heater is not providing enough hot water, people usually think that the unit started falling apart, producing less hot water with lower efficiency, so they either call a plumber to repair it or buy a new heater. 

What about DIY?

So, before you spend money, let's first look at the causes affecting hot water production and how to prevent and troubleshoot them. Some of these problems are an easy fix; some require knowledge, experience, and the right tools.

There are several reasons why you might be running out of hot water faster than before:

Sediment buildup

Sediment buildup often occurs due to hard water or mineral presence in the water. Over time and due to increased operating temperatures, minerals can accumulate at the bottom of the tank. As time goes by, and if the water heater is not maintained regularly, the buildup can grow to the point that it can significantly reduce the heat transfer between the gas burner and water inside the tank. Similar applies to electric water heaters with heating elements that are covered with limescale deposits.

If sediments are present, it will decrease the amount of water that can be produced, followed by the loud rumbling noise.

The solution for this problem includes regular tank flushing and installation of a water softener. If you don't maintain a water heater as recommended by the manufacturers and experts, an insufficient supply of hot water is not going to be the only problem, but it might lead to corrosion and leakage.

The temperature is set too low

If the temperature is set too low, this is an easy fix. Keep in mind that incoming water during winter is colder than during summer, so if your hot water is not as hot as it used to be, increase the temperature on the thermostat to your liking.

If you have an electric water heater, one of the thermostats or elements might not be working, resulting in poor heating and not enough hot water in your shower. Replace the element if needed.

Another solution is to install a mixing valve, designed to mix cold and hot water, and provide the temperature you selected without the risk of scalding or taking less comfortable (cold) showers.

Thermostats are designed to operate in a range from 100 to 140 F, but when a water heater is shipped to your home, thermostats are set on 120/125 F, so try to keep it that way, or slightly higher if needed. If your water heater doesn't have a temperature dial with degrees on it, but warm, hot, very hot, and vacation settings, choose the one that suits you best.

Broken dip tube

A dip tube is the plastic pipe connected to the water inlet on one side and with the other end submerged in water, a few inches above the tank's bottom. It is designed to bring cold incoming water to the bottom of the tank, where it gets heated. With an increase in the temperature, the heated water rises to the top of the tank, from where it gets transferred to the shower, hot water tap, dishwasher, or any other application.

If the dip tube is broken, cold water cannot reach the lower part of the tank; it mixes with hot water in the upper part of the tank, so only tepid water gets drawn to the faucet or a shower.

A solution to this problem is to replace a broken dip tube.

Undersized water tank and high demand

Do you know that your water heater can become "undersized" for your needs? How, you would ask?

If you have a growing family, kids becoming teenagers, guests, several applications running simultaneously, an upgrade such as a Jacuzzi or spa, your water heater might not be able to cope with the high hot water demand. It slowly becomes unfitted for your new household setup, incapable of delivering enough hot water.

There are few solutions for this problem, such as adding a new smaller unit such as POU (point of use type), increasing the flow, or getting a larger tank or tankless type, with an endless supply of hot water. When it comes to sizing a water heater, check out the article to better understand what you need.

The heat source is compromised

The heat source of a gas water heater is the gas burner, while the electric models utilize heating elements.

If the problem is with a gas burner, you can recognize it by looking at the flame pattern and its color. The flame should be stable and have a light blue color. If not, a gas burner might be getting too much gas pressure, it is dirty, or condensation might be dripping, affecting its performance.

In a case of an electric water heater, heating elements might be covered with limescale, worn, or simply malfunctioning, generating much less heat than before.

How to check is there enough hot water

You can use the following test to check if there is enough hot water. The tests are easy to follow but are time-consuming. No need to call a plumber or service personnel and spend hundreds of dollars, just go through these steps. These procedures can be applied to residential water heaters using natural gas and made either by AO Smith, Bradford White, Rheem, or any other manufacturer.

Let's make two assumptions here; the water heater is operated by natural gas, and it has a capacity of 50 gallons.

It is essential to say that according to the heater's manufacturers, the maximum available volume of hot water is lower than the unit's capacity. That means a 50-gal water heater does not contain 50 gallons of hot water. The unit will deliver approximately 70% of the tank's capacity. If we take, as an example, a 50-gal water heater, there will be 70% of 50 gallons of hot water available, and that equals 35 gallons (0.7*50=35 gal).

If the capacity is unknown, check out the rating plate found on the heater.

Next, if the temperature on the thermostat is set to 120 F, the temperature could be between 100 F and 120 F (approximately 20 F difference).

Draw test

This procedure is called the Draw Test, and there are two parts of the test. The water heater should be fully recovered from the previous use.

First, discharge one cup of hot water by opening the temperature and pressure relief valve (T&P valve), filling the cup at the free end of the discharge pipe. The hot water temperature inside the cup should be hotter than the set temperature, at least by 10 F. If it is lower, something is wrong.

Next, use the 5-gallon bucket to collect hot water from a heater. Do it several times until the capacity reaches approximately 70% of the tank size. After every draw, measure the temperature of hot water. The temperature of hot water in the last draw should be within 20 F of the thermostat setting. If it is not, there is a problem.

Other things to consider

When dealing with insufficient hot water, it is also a good idea to check your showerheads and other fixtures, as you might have a low-flow type. For the water heater with the capacity of 50 gallons, and after applying the 70% rule, 35 gallons of hot water is available (thermostat is set to 120 F). The recommended shower head flow rate is around 3 gallons per minute, which gives you approximately 10-15 minutes of showering. So, check the shower head flow rate before calling a technician.

If your water heater is not producing enough hot water for you and your family, not only that it can make it difficult and uncomfortable to take a shower, clean the dishes and clothes, but it can be a sign that something bigger is going on. That is why proper and regular maintenance is important – to prevent problems. If you need help with your water heater, contact a professional plumber.

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