11 Reasons Your Water Is Only Lukewarm

Amy Pawlukiewicz
Written by Amy Pawlukiewicz
Reviewed by Jeff Botelho
Updated October 5, 2021
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Lukewarm water heaters are no fun, especially when all you want is a long, hot shower

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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 the problem can be fixed as a DIY project, and other times, a professional should be called in 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 10 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
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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 hot water heater to make sure it’s set to the correct temperature, but be sure not to go over 120 degrees or you risk the water being too hot.

2. 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.

When this happens, there’s not a great DIY solution. Call a hot water heater repair professional near you to replace your thermostat.

3. Sediment Buildup in theTank

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.

4. 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. 

5. Your Water Heater Is Too Small

If you’ve moved into a new home, installed a hot water heater yourself, or added bathrooms or babies to your house, 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.

6. 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? Space out your chores. Run your dishwasher and washing machine at separate times, ideally when no one in the house is showering.

7. 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. Install low flow faucets and showerheads to conserve water and increase the amount of hot water that gets to your tap.

8. 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 element.

9. 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.

10. A Broken Dip Tube

The dip tube 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. Contact a pro if you suspect a broken dip tube.

11. 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.

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