Hot Water Heater Only Lukewarm: Causes, Fixes and Prevention

Disclaimer: This post may contain affiliate links, meaning we get a small commission if you make a purchase through our links, at no cost to you. For more information, please visit our Disclaimer Page.

Imagine on a cold winter day, as you step into the bathtub and turn on the hot water tap, a cold surprise awaits you.

Or in this case, a lukewarm surprise. But the idea is the same, since what you expected when using the hot water tap is warm or hot water, not the temperature you're currently getting.

On the other hand, you might want to wash your dishes using hot water and the same thing may occur so you will not be able to finish your washing.

In these and many other similar cases, the water heater is showing signs of malfunction and causing you some serious issues which may make your bathroom or any other faucet useless.

In case of lukewarm water flowing from your faucet when you are using hot water tap it is very important to stay calm, diagnose and fix the problem as soon as possible and prevent it from causing you more difficulties.

Hot Water Heater Only Lukewarm

What Is Preventing The Water From Fully Heating?

If the water flowing from the hot tap is not that hot, it doesn't necessarily mean that the water is not heating at all.

Sometimes a certain malfunction could occur and prevent the water from heating enough before it exits the faucet.

In other cases, it is also possible that the water in your heater is mixed, in a way that makes the cold water run before the heated water.

On the other hand, the problem might not be related to the heater itself at all, but with other components of the heating system, or in the pipe that is connecting the cold water supply to the heater.

There are a lot of possible causes of this problem, so the best thing to do at the start is to try and figure out if your issue was triggered by any of the most usual reasons.

Causes of Lukewarm Water from Hot Water Heater

Here is a list of the most common causes of lukewarm water flowing from the hot water tap.

If you can’t relate your problem with any of these reasons, your best option is to hire professional help.


One of the immersion heaters might have stopped functioning

There are in most cases two immersion heaters located in the cylinder and if one of them malfunctions, it could easily be the reason for your lukewarm water.

In case one of the immersion heaters malfunctions, the other one will still try to overcome that loss and heat the water.

Since one heater is not enough to warm up all of the water in the cylinder, the resulting water flowing from your hot water tap will be lukewarm.

This is one of the most common water heater issues that is hardly exposed.

Check if the thermostat is causing you difficulties

If you have a water-based heater, your problem might be with one of the thermostats.

Your heater has two cylinder thermostats, located differently depending on the manufacturer.

Be sure to check both of the thermostats, since malfunction of even one could make an issue such as lukewarm water flowing from the hot water tap.

Another thermostat malfunction that could occur is the fault in the measurement system, where your thermostat may show the wrong temperature and make the cylinder stop warming the water before it is warm enough.

This may result in lukewarm water flowing.

A tripped breaker is causing your heater to stop working

There is a possibility that you hadn’t spotted that the breaker responsible for your heater was tripped.

This may result in a stoppage of water warming in the cylinder.

On some types of cylinders, the water warmed inside it may remain lukewarm for days before it becomes cold.

If the breaker was tripped, and the heater stopped working that might be the reason for lukewarm water flowing.

Return it to its position and check to see if the heater has started warming up the water again, to check if this was the cause.

Dip Tube Malfunction

This is potentially the most dangerous cause of lukewarm water.

The Dip Tube is a component of a water heater which is regulating the water flow in the heater, making sure that the cold water is always located at the bottom of the tank is heated up since the hot water is located at the top of the tank from where it goes out into your faucet.

If for some reason it stops conducting its purpose, the cold water will remain on the top of the tank, that way exiting the tank before the hot water, so you will always get lukewarm water when using the hot water tap.

This malfunction has proven very dangerous since in case it fails, you will probably have to replace the whole tank.

Mineral Deposit Buildup in the tank

What you probably wouldn’t guess is that mineral deposits can also form even in your heater tank.

The water entering the tank may carry those deposits as well as some other substances, which will make it impossible for the heater to work correctly.

The minerals buildup may prevent water from entering the tank, as well as making it more difficult for the heater to warm up the water.

Since most of the heaters are located at the bottom of the tank, this may make it impossible to warm up the water.

How to Fix Heater Lukewarm Water Issues

After you have successfully determined the cause of the problem, your next step is to do what you can to save yourself from having to replace the whole water heating system.

Of course, some causes require easier solutions, while some of them might make it impossible for you to do anything.


In case your thermostat gives you problems, you can try to find the right replacement and replace it yourself.

The important thing is to figure out which thermostat was the problem and replace only that thermostat with the right one.

In the case of a tripped breaker, you can easily fix the situation by flipping it to the right position.

This requires the least possible work so hopefully, it will be the reason why your heater is not working correctly.

In the case of the Dip Tube malfunction, your best choice is to hire professional help and replace the entire tank.

The position of the Dip Tube makes it hardly reachable, so there is no point in trying to replace this malfunctioned component with a new one.

In the case of mineral buildup in the bottom of your heater tank, your best choice is to hire a plumber as well, since it is hard to reach the spot where minerals could be accumulating.

You can try using chemical agents against mineral deposits to prevent the future accumulation of the same thing which was the cause of your water not being warm.

Overall, most solutions when it comes to fixing malfunctioned water heater require professional assistance, since the components in the heater are not that durable and easy to reach or replace.

If the solution requires professional help, you should not try to fix something yourself and possibly make it even worse.

How to Avoid Lukewarm Heater Water Issues

There are not too many things you can do to prevent issues like this from occurring again.

You should constantly check the thermostat temperature of your heater, to make sure that the temperature is operational.

Use chemical agents for cleaning your pipes, since the water moving through the pipes accumulates minerals and bacteria that could prevent the heater from warming up the water.

You should also never heat more water than you need since by leaving warm water in the cylinder you might not notice the malfunction of heater since water can stay warm for days in the tank.

The heater is one of the plumbing components that are very difficult to maintain on your own.

For that reason, the best thing you should do is clean the pipes and check the temperature as often as you can.

Conclusion: Hot Water Heater Only Lukewarm

It can be very annoying to have lukewarm water flowing from your hot water tap, therefore preventing you from conducting your daily routines.

We often take components such as water heater for granted, so we don’t even pay attention if it is working the way it is supposed to.

Either way, there is not much you can do in case this malfunction occurs, but you can do your best to find the source of the problem and recommend a solution, or hire a plumber.

This article contains crucial information regarding recognition of what has caused the problem, as well as some advice on how to help lower the damage yourself.

There are certain activities mentioned in the article that would help in the future preservation of your water heater and its functionality, but the best advice given is certainly to know when it is time for consulting with the professionals.