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Water Heater Not Staying Hot? Top 8 Reasons (+ How to Fix!)

When your water heater doesn’t work, you’re stuck with cold showers and sinks. There are many common reasons water heaters stop working or lose their heat quickly. If you’re stuck with a cold water heater, it’s only going to get worse.

Your water heater won’t stay hot for these reasons:

  • Not enough gas or electricity
  • Mineral buildup
  • Broken thermostat
  • Pressure concerns
  • Pilot light problems
  • Worn dip tube
  • Low PSI
  • Plumbing or tank leaks

In this article, we’ll dive into several explanations for why your water heater won’t stay hot. We’ll also talk about what you can do about it and whether or not your unit needs to be replaced. Enjoy!

Low Gas or Electricity

Low gas flow or electricity can limit your water heater’s performance. Check if your water heater uses gas or electricity. Almost all water heaters have electrical components to spark a flame, but some of them are solely electrical. These two fuel sources are required for a water heater to maintain hot water.

These factors contribute to reduced gas or electricity:

  • Worn or broken gas lines (the rest of your house will likely have symptoms, too)
  • A broken circuit breaker or wires going to the water heater
  • Unpaid utility bills that limit gas and energy
  • Corrosion, rust, and buildup in the gas lines

How to Fix

Here’s a list of suggestions to fix gas or electric problems for your water heater:

  • Hire a professional to inspect all of the gas lines to look for leaks since they can be hazardous and expensive if they go unchecked.
  • Test the circuit breaker with a multimeter to ensure it’s getting enough electricity, then replace it if necessary.
  • Ensure all of the utility bills are updated and contact the company to find out if there’s a supply issue.
  • Inspect the gas lines for corrosion and rust since they can leak gas and reduce the heat coming from your water heater.
  • Check if the gas valve going to the water heater is open all the way since a shut or semi-closed valve reduces the fuel source.
  • Look for broken or disconnected wires in and around the water heater, especially if you have an electric unit.

Mineral Deposits in the Water Heater

Pete the Plumber states minerals can build up inside of the water tank. Manganese, calcium, iron, and other minerals naturally found in local water sources contribute to this buildup. When the minerals pile up, the water pressure is reduced. They can also prevent the water from getting hot enough without warning the thermostat.

If your water heater is old, there’s a high chance that it could have mineral issues. These minerals typically take a long time to build up, but it depends on your water supply. Test your tap water for minerals to know if you need to clean or flush the water heater more often than usual.

How to Fix

Removing mineral deposits from your water heater can dramatically improve its performance. Below, you’ll find the step-by-step instructions.

  1. Turn off the electricity and gas valve going to your water heater to prevent hazards.
  2. Connect a garden hose to the water heater’s drain.
  3. Drain all of the water out of the water heater into a tub, looking for sediment.
  4. Refill the water heater with water and drain it again to agitate and flush the system.
  5. If there’s a lot of sediment in the second draining session, repeat the previous step.
  6. Close the drain valve, refill the water heater, and turn on the electricity and gas valve.

Water heaters naturally build up mineral deposits from the minerals found in your water supply. It’s essential to flush the system at least once per year. They can prevent iron from rusting the inside of the water heater, which could corrode and deteriorate the unit.

AmplifyDIY provided a helpful video you can use, too:

Malfunctioning Thermostat

A broken thermostat is often the most common cause of a malfunctioning water heater. If the thermostat is broken, the water won’t be set at the desired temperature. Unfortunately, a broken or damaged thermostat reports false readings. These settings tell the water heater that the water is hotter or colder than it is.

The thermostat is perhaps the most important part of the process. Without a properly functioning thermostat or a thermometer, nothing can heat the water. This scenario is usually quite slow, which is why the water doesn’t stay hot as long as it used to, then shortens over time. If the thermostat shorts, it could be an instant and permanent temperature drop until it’s replaced.

How to Fix

Replacing a water heater’s thermostat can make a world of difference. Let’s go through the easiest method here:

  1. Turn off the power going to the water heater at the circuit breaker.
  2. Locate the thermostat in the owner’s manual (it’s usually behind the front panel near the control board).
  3. Disconnect the thermostat by removing the mounting screw and the two wires connected to it.
  4. Insert and mount the new thermostat with the mounting screw and two wires from the previous step (always use the part number recommended by the manufacturer).
  5. Attach the panel and turn on the power at the circuit breaker, then test your work.

The easiest way to know if the thermostat is working is to test it with a multimeter. The AstroAI Digital Multimeter has a red and black node. Touch these nodes to the two wires going to and from the thermostat. If they don’t show 110v to 220v (depending on your water heater’s required voltage), it’s time to replace the thermostat.

Pressure Relief Issues

Every water heater has a pressure relief valve (also known as a temperature relief valve). These valves are crucial because they prevent too much PSI from building inside of the tank. However, the valve can corrode or get stuck. When it doesn’t move or open, you might not be able to stop cold or hot water from flowing through.

Fortunately, you can replace the pressure relief valve quite easily. It takes a few minutes to drastically improve your water heater’s performance. This simple process usually requires plumber’s tape (Teflon tape), silicone sealant, and a like-for-like water heater pressure regulator.

How to Fix

Follow this simple procedure to replace a temperature-pressure relief valve:

  1. Turn off the gas, electricity, and water flowing through the water heater.
  2. Drain the water with the steps mentioned above (using a garden hose).
  3. Twist the valve counterclockwise with a wrench to remove it.
  4. Remove the Teflon and sealant from the threaded pipe beneath the valve.
  5. Wrap the threaded portion with a new layer of Teflon tape, dab it with silicone sealant, and twist on the new like-for-like valve.
  6. Fill the tank with water, turn on the utilities, and open the valve to test your work.

Pilot Ignition Problems

Your water heater’s pilot light is solely responsible for increasing the water temperature. Gas-powered water heaters combine a spark with gas to create heat. Electric water heaters use electricity to warm the pilot light. When the pilot light doesn’t have enough fuel, or it’s broken, you won’t be able to heat the water as quickly.

If the pilot light is damaged or bent, it’ll keep your shower or sink water warm for a few minutes. As the heated water leaves the tank, the poorly-functioning pilot light can’t keep up with the heat demands. Pilot lights worsen over time, so it’s important to fix or replace them as soon as you notice the issue.

How to Fix

Many pilot ignition problems are caused by misalignments and damaged components. You can fix them by using pliers to point the lighter at a 45-degree angle inward. The spark and gas have to meet perfectly to create a light. If they don’t, the water heater won’t get warm.

Always ensure the gas and electricity are off before working on the pilot light. Low gas problems will inevitably lead to reduced temperatures because there’s not enough fuel for the ignition. If the pilot light looks fine and there’s enough electricity, chances are there’s not enough gas flowing to the pilot.

Note: Damp pilot lights won’t ignite. Check if there’s moisture on or in the light before replacing it.

Misaligned Dip Tube

The dip tube sends cold water from the ground into the water heater. The water flows to the bottom of the hot water tank and gets warm, then flows through the pipes to your home.

According to Ragsdale Air, the dip tube can break or become misaligned. This misalignment sends the water over the bottom of the tank, which prevents it from heating. Your water will either be lukewarm or cold.

The dip tube rarely carries hot water, but it’s an essential part of carrying new water to the tank. A broken tube can drop the pressure, which causes additional problems (all of which we’ll cover in the following section).

How to Fix

Here’s the process to fix a broken dip tube:

  1. Turn off the water, gas, and power going to the water heater.
  2. Use channel locks to remove the cold water line from the dip tube going into the top of the tank.
  3. Untwist the old dip tube and remove it from the tank.
  4. Wrap the threaded portion of the new dip tube, then slide it into the tank and twist it until it’s sealed.
  5. Use channel locks to connect the newly installed dip tube to the waterline, then turn everything back on to check if it leaks.

If you prefer a video guide, here’s one from Pros DIY on YouTube:

Reduced Water Pressure

Does your water pressure seem lower than usual? Reduced pressure (also known as PSI) lowers the amount of water going to the bottom of the tank. If the water doesn’t reach the tank’s far end, it won’t get hot enough for a long time. Armstrong Comfort shows reduced water pressure is a leading cause of why your water heater won’t stay hot.

Here’s a list of possible causes:

  • Mineral buildup
  • Leaks in the plumbing
  • City or well water pressure reduction
  • Too many sinks, showers, toilets, and other appliances using water simultaneously
  • Backed up water pushes the water back into the cold water pipes without heating it

How to Fix

Try these suggestions to fix low water pressure:

  • Locate and patch all leaks with plumbers tape and silicone sealant (replace broken pipes; Don’t try to epoxy them!).
  • Only use one or two water features in the house at the same time.
  • Ensure the water valve is completely open going into and out of the water heater to prevent it from lowering the pressure.
  • Follow the aforementioned procedure to flush the system to remove mineral buildup.
  • Contact the city water supplier to find out if there’s a citywide water pressure issue.

Leaks in the Plumbing

Plumbing leaks cause the water pressure to drop. As we showed above, lower water pressure typically reduces the heat coming out of the water heater. These leaks can be found in the pipes going to and from the water heater. However, some of them are found on the shower nozzle or tub faucet.

If there’s water leaking from the water heater, you’ve likely found the problem. Keep in mind that condensation is natural, but there shouldn’t be liquid dripping from the bottom of the water heater. Look for leaks along the pipes outside, too.

How to Fix

To fix a leak between connection points, follow these steps:

  1. Turn off the water and close the water pressure valve.
  2. Use channel locks to loosen the connections.
  3. Use a like-for-like elbow or coupling between the two pipes, ensuring you cover all threaded portions with Teflon tape and silicone sealant (if they’re PVC, use blue glue).
  4. Hire a professional plumber if your pipes are made of copper and need to be soldered.

To fix a leak on a pipe, it’s best to get a new pipe of the same dimensions. Some homeowners use epoxy as a temporary fix, but this decision leads to bigger leaks and reduced water pressure.

Additional Water Heater Resources

To learn more about water heaters, check out some of our other articles about water heaters:


  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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