15 Reasons Your Water Is Only Lukewarm

Lukewarm water heaters are no fun, especially when all you want is a long, hot shower

Woman runs hand under water
Photo: LaylaBird / E+ / Getty Images
Woman runs hand under water
Photo: LaylaBird / E+ / Getty Images
Allie Ogletree
Written by Allie Ogletree
Contributing Writer
Jeff Botelho
Reviewed by Jeff Botelho
Journeyman Plumber, Harold Brothers Mechanical Contractors, Inc.
Updated February 6, 2024

Highlights

  • Rule out the easy fixes before moving on to the more complicated and costly ones.

  • A faulty or too-low thermostat is a common cause of lukewarm hot water.

  • A higher demand for hot water can cause smaller tanks to run out.

  • Repairing a water heater costs around $590, while a new unit costs around $1,300.

  • Contact a plumber if you can’t fix your water heater.

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There are several reasons your hot water heater might be cooling off, and there are signs you can look for when your water heater is about to fail. Sometimes you can turn up the temperature on your water heater. Other times, you’ll need to call in a professional for the fix. The national average cost to hire a professional to fix a water heater is $590, with most repairs falling between $225 and $960. Learn 15 common reasons your hot water heater is only lukewarm and possible solutions to those issues.

1. The Thermostat Is Too Low

Turning up temperature on electric water heater
Photo: surasak / Adobe Stock

To save money and conserve energy during the summer, a lot of homeowners turn down the thermostat on their hot water heaters. The trick is, in the winter, you have to remember to turn it back up. Luckily, this one’s an easy fix.

Check the thermostat on your water heater and your manufacturer’s recommended range to make sure it’s set to the correct temperature. The ideal temperature to save on energy is 120 degrees Fahrenheit, but you can usually crank the heat up to as much as 140 degrees. 

Note that some people who are immunocompromised need higher temperatures for health reasons. Meanwhile, people who live in a multi-family home may need the increased temperature for the water heater to keep up with the demand for hot water.

2. Tripped Breaker

If your water heater started out hot only to go lukewarm, then to room temperature, and now cold, then it’s probably a good idea to check the breaker or fuse box. If you have a tripped breaker or blown fuse, the water in the tank could still stay warm for several days before losing all heat. This can make it seem like there’s a technical problem with the equipment when, really, you just don’t have power.

The fix for this one is to flip the switch back to “ON” or replace the blown fuse. If you notice other electrical problems or the circuit continues to trip, then you may need to call in an electrician near you to get to the root of the issue. Don’t attempt to repair electrical wiring yourself—especially if water-using appliances are involved—as this can put you at risk of electrocution. 

3. The Thermostat Is Broken

If you turn up the thermostat on your hot water tank and don’t feel an increase in water temperature, there’s a chance your thermostat is broken. You can test your water heater thermostat with a multimeter to see if it requires replacement. If it does, there’s not a great DIY solution. Call a hot water heater repair professional near you to replace your thermostat.

4. Sediment Buildup in the Tank

Water that enters your water heater carries particles like dirt and sediment with it, and eventually, those can build up in the tank. Because the buildup happens at the bottom where the heater is, sediment buildup can lead to lukewarm water production. Hard water carries more minerals than soft, so if you live in an area with hard water, this could be the culprit. To get the hot water flowing again, drain the tank and consider installing a water softener.

5. The Tank Is Leaking

Though it may not be visible, your water tank may have sprung a leak. If you suspect a leak, call a professional. Do not try to repair this yourself, even if you’re a DIY die-hard. Incorrectly replacing a leaky valve under your water heater can lead to more leakage, which could puddle on your floor and cause mold and mildew or structural damage to your home.

6. Your Water Heater Is Too Small

If you’ve moved into a new home, installed a hot water heater yourself, added bathrooms, or expanded your family, you may have ended up with the incorrect size for the demand of your home.

If you’re tired of jockeying to be first in line for the shower, consider a tankless water heater, which could be 24% to 34% more energy efficient than a traditional water heater. Tankless water heaters can also save space, as they don’t store hot water but heat it on demand for each use.

“While tankless heaters are a great choice when replacing your water heater, it is imperative that they are maintained at least annually to guarantee that they continue to perform at peak efficiency for years to come,” says Jeff Botelho, Expert Review Board member and licensed journeyman plumber.

7. Too Much Demand

If you’re running your washing machine, dishwasher, and bathtub all at once, you may be creating too much demand without enough hot water supply. The fix to hot water not working? Space out your chores. Run your dishwasher and washing machine at separate times, ideally when no one in the house is showering.

8. Your Faucet’s Flow Rates Are Too High

The flow rate refers to the gallons per minute (GPM) your hot water tank is producing to keep up with the demand in the house. If the flow rate for each faucet is high, not enough hot water will get to each tap. This could be one reason you have no hot water with a tankless water heater. Install low-flow faucets and showerheads to conserve water and increase the amount of hot water that gets to your tap.

9. A Broken Heating Element

Electric water heaters usually have two heating elements, and if one of them breaks, the other has to make up the difference. This lack of efficiency can result in lukewarm water from your faucets. Regular maintenance can stave off a failure, but in the event one goes bad, call in a pro to replace the faulty water heater element.

10. A Broken Gas Valve

The valve in gas water heaters usually lasts around 10 years, after which it becomes susceptible to damage. If you notice a funny smell like garbage or rotten eggs, that’s an indicator that your gas valve has broken and there’s a leak.

The solution? Call in a professional and possibly your gas company. Gas valves cannot be repaired, so if there’s a problem with your gas valve, it will need to be replaced. Gas is extremely dangerous to work with if you don’t have the proper professional training, and performing a repair incorrectly can lead to a leak, which is not only a health hazard if you’re inhaling it, it can also lead to an explosion. Seriously, don’t try to DIY this one.

11. A Broken Dip Tube

The dip tube, also called the anode rod, pushes cold water down into the bottom of your tank to be heated. When the dip tube malfunctions, the water doesn’t get pushed down into the heating mechanism. As a result, your heater becomes less efficient and more likely to put out lukewarm H2O. Dip tubes last around eight to 12 years on average, so it’s possible that the dip tube needs replacing a few years before your water heater. Contact a pro if you suspect a broken dip tube.

12. Cross Connections

Cross connections, where potable water comes into contact with non-potable, usually occur in older plumbing systems. Since these problems usually occur outside your home, they are difficult to identify until you’ve ruled out other problems. If you have eliminated other possible causes of your water heater only producing lukewarm water, a cross connection may have occurred when the city was updating plumbing near your home. You should contact your plumber and your city if you suspect this is happening.

Botelho says another type of cross connection that can cause your hot water to cool down is when a mixing valve or a recirculating system fails. Mixing valves allow hot and cold water to mix together and if the mixing valve fails, this can cause water to pass through it when it is turned off. This, in turn, allows hot water to migrate into the cold water side, reducing the amount of available hot water when another fixture or faucet is turned on.

13. Not Enough Insulation

If you notice your water is not getting hot enough in the wintertime, then it might be a matter of poor insulation. Homes in extremely cold climates may need insulation to prevent heat from slipping away from the water heater. Even homes in warmer climates can feel the impact of a cold spell on a hot water heater as it struggles to perform at its usual capacity. The best solution for this issue is to insulate your water heater

Pipe insulation may also help prevent the water from cooling as it flows to your faucets.

14. Clogged Pipes

Your water heater might not be the culprit. If you have a clogged pipe, this can cause a low hot water pressure, which may make it seem like the water heater isn’t working. In reality, it’s really a pipe at fault. One telltale sign that you have a clogged pipe on hand is lower water pressure or hot water temperature issues from only a single source.

If the temperature is low enough for pipes to freeze, usually in the 20-degree zone or colder for prolonged periods, then your clogged pipe could be a frozen pipe. Be sure to winterize your home ahead of time and unfreeze the pipes before they burst.  

15. Water Heater Is Near the End of Its Life Span

Sometimes, it’s simply the end of the line for your water heater. Like any appliance, water heaters have a limit to how long they last and how efficient they are toward the end of their life spans. The average water heater life span is 10 years but can range from six to 15 years depending on the brand, how well you maintained it, the water hardness level, and the demand. 

If your unit is reaching the 10-year mark, it might be time to replace your water heater with a newer, more efficient model. It’s best to contact a local plumbing company if you have concerns about your water heater or want to replace the unit. The typical cost to replace a water heater is $900 to $1,800 or $1,300 on average. 

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Learn more about our contributors
Allie Ogletree
Written by Allie Ogletree
Contributing Writer
Allie is an Austin-based content writer specializing in home improvement, renewable energy, and deregulated energy markets.
Allie is an Austin-based content writer specializing in home improvement, renewable energy, and deregulated energy markets.
Jeff Botelho
Reviewed by Jeff Botelho
Journeyman Plumber, Harold Brothers Mechanical Contractors, Inc.
Jeff Botelho has 18 years of experience in the plumbing trade and specializes in installing and maintaining ultra-high efficiency, commercial and residential hydronic space heating and water heating systems.
Jeff Botelho has 18 years of experience in the plumbing trade and specializes in installing and maintaining ultra-high efficiency, commercial and residential hydronic space heating and water heating systems.
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