Hot Water Just Lukewarm? Why and What to Do

Why s My Hot Water Lukewarm?

A water heater is best suited to perform at 120 to 130 degrees Fahrenheit. At that temperature, the water is hot enough for your needs and kill the bacteria in the tank but will not scald.

If you notice that your hot water is no longer as hot as it used to be and is just lukewarm, you definitely have a problem with your water heater. The good thing is that most water heater problems are things you can easily fix on your own.

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If your hot water is not hot enough but just lukewarm, it is a sign of a tripped water heater breaker/reset button, sediment build up in the tank, broken dip tube, faulty thermostat or burnt out element. It also happens when the pilot light is out.

As you can see from the statement above, the problem can be caused by a couple of factors. The best course of action in this case is to troubleshoot the water heater by eliminating one thing at a time.

Although in most of the cases the problem is caused by an issue with the water heater, it could be caused by cross-connected pipes if you live in an old house with old plumbing. In this is the cause the solution will be a rather expensive one.

If you have a brand new water heater and the water is just lukewarm, most likely the thermostat was not properly adjusted during installation. It could also be that one of the heating elements burnt out during installation especially if the heater was tested on an empty tank.

Let us now go deep in detail and see why you are having no enough hot water and how to fix the problem.

1.Tripped Breaker

This will affect electric water heaters.

Every appliance in your house has its own dedicated circuit breaker at the main electrical panel. In case of an unsafe condition like a power surge, the breaker will trip shutting off power to the appliance.

In the case of a water heater, the breaker or reset button will trip in case of such a condition. When that happens, power to the heating elements will be turned off and you will only have lukewarm water which become even cold unless the problem is fixed.

Dash to your house’s electrical panel and look for the breaker named “Water Heater” or with the initials “WH” on it. Check if it is on the on or off position.

If the water heater breaker is in the off position, it has certainly tripped. Flip it back to the on position and observe it for a while.

If it remains in the on position then your problem is fixed. On the other hand, if it flips back to the off position you have a problem with either the reset button, thermostats or heating elements.

If the water heater breaker is in the on position, the breaker is not the problem. Flip it to the off position to be able to work on the water heater.

Note that there will be 240 volts flowing to your water heater and working on it with live power is very risky.

2. Tripped Reset Button

A water heater reset button, also known as an emergency cut off switch will turn off power to your water if the thermostat fails to do so. It does so when the water temperature in the tank exceeds 180 degrees Fahrenheit.

To access the water heater reset button, you will first need to remove the water heater top access panel. Electric water heaters have 2 heating elements and 2 thermostats. The reset button is usually on the upper thermostat which is on the upper access panel.

  • Remove the upper access panel cover plate using a screwdriver.
  • With the cover out, you will see a piece of insulation. Lift it off and secure it against the tank using electrical tape.
  • Remove the plastic piece which snaps on both the thermostat and heating element.

You can see the reset button which will in most cases be a red button.

To reset the water heater, press the reset button until you hear it click. If it doesn’t click, you will need to press it and hold for about 5 seconds.

Note: Resetting a water heater only works if the reset button has tripped. If the reset button looks good, go ahead to test the thermostat and heating element for continuity.

3. Faulty Thermostat

The function of a thermostat is to turn the heating element on and off. When one of the 2 thermostats is faulty, your hot water will not be hot enough.

Your water heater thermostat is the little device with a series of screws and wires connected on them. Upper thermostats are usually different from lower heating elements.

Before testing the water heater thermostat for electrical continuity, you need to first check at the temperature indicated by the temperature adjustment dial. This especially makes sense if you have a new water heater whose hot water is only lukewarm.

The temperature adjustment dial looks like a big plastic screw. Use a flathead screwdriver to turn the dial and adjust the temperature to your desired settings (usually 1200 F).

If the temperature adjustment dial looks good, you could be dealing with a faulty thermostat. The only way to establish that is by testing it for electrical continuity using a multimeter. You will need to test the lower and upper thermostats.

I have written a comprehensive post on how to test and replace a water heater thermostat. Read it here.

4. Faulty Heating Element

Your hot water could be lukewarm because one of the heating elements is burnt out or shorted. The water heater element is found just below the thermostat with 2 screws and 2 wires connected around them.

Again, you will have 2 heating elements, an upper and a lower heating element. Testing a water heater element for continuity is the only way to establish if is faulty or not.

A faulty water heater element will need to be replaced. I have written a detailed guide on how to test and replace water heater elements. Read it here.

5. Pilot Light is Off

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A gas water heater has a pilot light which is responsible for making sure that the burner is on. When the pilot light goes off the burner goes off as well.

The above is made possible by a thermocouple. The thermocouple is placed very close to the pilot light while its other end is connected to the gas valve.

The heat from the pilot light generates a voltage in the thermocouple which activates a spring to open the gas valve, and therefore gas flows to the burner.

 When the pilot light is off, the voltage in the thermocouple drops, a move which turns off the gas valve meaning no gas will flow to the burner. When this happens, you will have lukewarm water which will then turn completely cold unless the pilot is light.

A very strong wind can also put out the pilot light. It could also be as a result of a dirty pilot light or a tripped thermal switch which turns off power to the pilot when the chamber is too hot.

I have written a detailed post on how to troubleshoot a faulty gas water heater. Read it here.

6. Sediment Buildup

The water flowing to your water heater has a lot of dissolved minerals especially if you live in area with hard water. Not all dissolved minerals that enter the water heater will flow out with the hot water.

Most of the minerals settle at the bottom of the tank. This is why you are advised to flush out your water heater at least once a year.

The sediment buildup at the bottom of the tank not only reduces your water heater’s capacity, but it also reduces the volume of hot water you are likely to receive. There also an increased risk of the water heater leaking from the bottom as the minerals corrode and eat away the tank.

The thing about sediment build up in a water heater is that it can completely trap a heating element, meaning that the heat will not be dissipated to heat the water and hence lukewarm instead of hot water.

The trapped heating element will also very likely burn out or short-circuit. In a gas water heater, the sediment buildup reduces the water heater’s efficiency meaning the sediment prevents heat from flowing to the water at the top of the sediment.

If you haven’t flushed your water heater for a long time, flushing it now would make little difference. You will most likely need to replace it.

I saw very cool video on You Tube of someone vacuuming sediments from a water heater through the heating element’s opening. Watch it here.

7. Broken Dip Tube

A dip tube is pipe connected to your water heater’s cold water supply pipe. It shoots cold water at the bottom of the tank where it is heated, while hot water occupies the top of the tank where it is readily available for use.

If the dip tube breaks off, instead of the cold water flowing to the bottom of the tank it will be delivered at the very top where it will mix with the hot water and hence lukewarm water.

The only solution for a broken dip tube is a replacement. To be honest, replacing a water heater dip tube is not very easy.

I found a really good video on You Tube explaining the steps you need to take to replace a water heater dip tube. Watch it here.

8. Old Water Heater

 A water heater will last for about 10 to 15 years on average. Electric water heaters last longer than gas water heaters.

So, how do you know how old your water heater is and if it is time to replace it? I have written an article on that very issue. Find it here.

9. Cross-Connected Pipes

This type of plumbing is found in old houses that have not been renovated in a long time. In cross-connected pipes, cold water is allowed to mix with cold water in order to balance out the temperature.

If you have cross-connected pipes, you may notice cold water flowing from your hot water faucet and vice versa

A house with cross-connected pipes will need a professional to fix. Sometimes if you use a mixing valve instead of a pressure-balancing valve in your faucet, the valve may fail, and the cold water will start pushing back into the hot water lines.

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