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Hot Water Heater Only Lukewarm – What To Do?

As a homeowner, some of the worst concerns you can face center around the water heater. If your water heater is only producing lukewarm water, the mounting concern over what has malfunctioned is likely making you anxious. Replacing or repairing a water heater can be costly and inconvenient. So what could be wrong? We've done some research and have some diagnostic and troubleshooting steps for you.

Disclosure: We may get commissions for purchases made through links in this post.

If a hot water heater is only producing lukewarm water, the problem could be one of the following:

  1. Sediment build-up
  2. No fuel
  3. No power
  4. Broken thermostat
  5. Faulty heating system
  6. Broken dip tube
  7. Hot water is depleted

Now that we've identified the most common problems causing hot water heaters to produce lukewarm water let's discuss each in more detail. We'll talk about troubleshooting steps, if applicable, and answer some other questions you might have. Keep reading to learn more.

An electric boiler, water heater on the blue wall, Hot Water Heater Only Lukewarm - What To Do?

What To Do When The Hot Water Heater Is Only Lukewarm

Let's further explore the top 7 issues causing your hot water heater not to fully heat up. 

1. Sediment build-up

The water entering your hot water heater contains natural minerals and sediment. As the water sits and heats in the tank of your water heater, those minerals become insoluble from the temperature and, in turn, settle to the bottom of the tank. Once this debris creates a layer in the bottom of the tank, it creates an insulating layer that blocks much of the heat from reaching the water, resulting in lukewarm water. Most water heaters have heating elements under the tank, which could explain your problem if the model you own is one of those.

To diagnose if this is the issue, stand close to your water heater and listen as it goes through a heating cycle. If you hear an abundance of cracks and pops that are beyond its normal functioning, sediment could be your problem. A professional repair person can flush the sediment out and resolve the issue.

2. No fuel

If you have a gas water heater, the solution could be as simple as checking your pilot light. A pilot light is what supplies the fire for the heating unit under your hot water tank. If the pilot light is out, then the burner has no way of lighting and heating the water tank. Most pilot lights are located right on the panel and should be self-evident. If you have trouble locating the pilot light, consult your owner's manual for more details.

Additionally, ensure a gas water heater is receiving fuel from your gas source. You can check this by seeing if your other gas appliances are working. If they aren't, the issue may be with the incoming gas instead of your water heater. 

3. No power

If you have an electric water heater, the issue could be a tripped breaker. If your water heater is silent and seems to have no power whatsoever, check your household fuses or breakers to ensure all is in working order. Replace any blown fuses or ensure the breakers are all in the "on" position. 

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4. Broken thermostat

The thermostat on a hot water heater is what regulates the temperature. If it's broken, your heating element might come on less or not at all. To determine if the thermostat is at fault, adjust your water heater's temperature to the highest setting and wait several minutes. If the water heating doesn't start the heating process, you likely have an issue with the thermostat. A service professional can repair a faulty thermostat for you. 

5. Faulty heating system

Electric water heats generally have a heating element at the top and the bottom of the water tank. If one of these fails, it can cause the water to come out lukewarm. Some water heaters have an immersion system where two heating elements are located inside the tank. If one of these stops working, the result is the same: water that doesn't quite get hot enough.

There could be something wrong with the burner located underneath the hot water tank for a gas system, causing it not to ignite.

Whichever type of water heater you have, if you hear it operating normally, but the water isn't hot, this could likely be an issue. A service technician can resolve the issue and repair the water heater.

6. Broken dip tube

A dip tube is located inside the water heater and directs water to the bottom of the tank for it to be heated. If the dip tube is broken and not circulating the water, this can result in cooler water. It allows the cool water to remain on top and the heated water to remain on the bottom. This issue is difficult to differentiate from some of the other issues causing the lukewarm water. If the issue is a broken dip tube, it's generally best to replace the whole water heater instead of repairing it.

7. Hot water is depleted

Sometimes the problem is the easiest one to fix: your hot water is depleted. Depending on the size of your hot water tank, the issue could be that you've used all the water heated and stored in the tank. If your tank is on the smaller size, a long shower can deplete it, and it takes at least 30 - 40 minutes for that heat to build-up again. Wait a while and try again after at least half an hour. 

What if I have a tankless water heater?

Tankless hot water heaters are great for giving hot water on demand, but they can still get overloaded. If you're trying to get hot water from multiple spots in the household simultaneously, this demand could cause the water only to be lukewarm. Many of the other issues we've discussed can affect a tankless hot water heater as well, such as no fuel, no power, bad ignitors, or bad heating elements.

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What should hot water heater temperature be set to?

A hot water heater shouldn't be set over 120 degrees Fahrenheit to prevent scalding. Many hot water heaters have a safety installed that will shut down the hot water heater if the temperature gets too high. This prevents any safety hazards. A regulated temperature also helps your energy bill.

How much hot water does a 10-minute shower use?

A 10-minute shower uses roughly about 20 to 25 gallons of water, depending on the type of shower head you're using. Some showerheads are designed with a lower flow to get the lesser end of the spectrum. These types of showerheads are more environmentally conscious and can cut down on your water bill.

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How long does hot water heater stay hot without power?

Once the power goes off, take a shower quickly if you were planning on one. The hot water heater only maintains the temperature for about an hour or two after its energy source has been eliminated. This number can vary based on ambient room temperature and insulation thickness on your hot water heater tank. A gas water heater is an advantage in this situation, as it will still work without power. 

Should you turn off the hot water heater while on vacation?

You can turn off your hot water heater while you're on vacation and save quite a bit of energy and cost on your next utility bill. If left on, it will continue to cycle to keep the water hot. For a gas water heater, shut off the gas supply to the tank. If the water heater is electric, you can shut off the circuit breaker controlling the hot water heater. 

Some hot water heaters have a vacation mode you can choose instead of shutting power off to the unit completely. Instead of shutting off the water heaters' connections, you can use this mode, or you can lower the temperature significantly on the thermostat so that the water heater won't cycle as much.

In Closing

Many different issues could cause your hot water heater only to produce lukewarm water, some easier to diagnose than others. Check as much as you can, and then reach out to the professionals for help if necessary. Here's hoping yours is an easy issue to identify and resolve!