Why Does My Tankless Water Heater Go Cold

Sometimes you may find water cold in your tankless water heater. Then you come on the net and start searching for the answer to a question, “Why Does My Tankless Water Heater Go Cold?” It happens because of several reasons like gas supply problems, dirty burner, bad ignitor, etc. Many people like to have a tankless water heater. It gives consumers some advantages more than a water heater with a tank. But it has a few opposing sides which are solvable.

By taking some easy steps, people solve their problems with tankless water heaters. Especially people with small accommodation problems love to use tankless water heaters for warm water. They are also inexpensive and available in local markets.

The tankless water heater is efficient and money saver. It does not need extra space for the tank and gives you warm water on demand. It is a continuous supply of water. Many people have replaced their water heaters with tankless one.

Before the invention of the tankless water heater, we needed to fill up the tank with water. Then give energy to them 24/7 and also required to preheat it. But with a tankless one, you can get hot water whenever you want it. It has 20 years of life expectancy.

Why Does My Tankless Water Heater Go Cold – 8 Common Problems

Coming to the answer to one of the most common questions, “why does my tankless hot water heater go cold?”. Some common problems and their expected solutions:

Wrong Installation

Proper installation is significant for your water heater. It is a little bit difficult too. Sometimes a bad plumber or by you try to install it at home or the office. As a result, some mistakes are made. So the water heater then faces difficulties to give you a good service for a long time.


Don’t try to install it by yourself. Get a good plumber who knows to install it gently.

Shorter Gas Lines

To accommodate warm water, gas lines should be extended. If it remains short, then the supply of water would be hindered. Extended lines help you to get instant hot water. It supplies a good service of water continuously.


Engage extended lines with your water heater replacing shorter ones.

Mineral Build-Up

You find mineral build-up in both water heaters with a tank or without a tank, but it brings damage to the water heater. The mineral build-up is increased by hard water.

Woman is checking temperature touching running water with hand for having a bath

Now you may guess what hard water is. It is the opposite of soft water. Hard water helps water with minerals and causes a problem in the water heater. It also decreases the quality of water.

Hard water contains calcium and magnesium, which help build minerals. . It reduces the quality of water. It also impairs the water heater’s function even without addressing it.


Always keep an eye on minerals. After every six months, flush your water heater. You can also use a water softener to avoid minerals. Don’t get to raise minerals high if you want good service from your water heater.

System Overloaded

The water heater system may get overloaded by using multiple water applications like multiple showering. It depends on your water heater capacity whether it could give service on various applications or not. It may struggle to supply water. Gradually becomes slow in service and gets shut down due to overload.


It would be best if you reduced warm water demand on multiple applications. You may need to reset your unit. Upgrading it or put a second unit also helps you to decrease overloads. It’s a little bit costly but will save your money in the long run.

Coldwater Sandwich

At the beginning of showering, you got some warm water, but a bunch of cold water drops on you after a while. This mixture of warm and cold water is called a cold water sandwich. It mainly happens due to a lack of timing.

The tankless water heater also takes a little time to warm water. At first, you got warm water, that’s trapped water in the pipe which was hot. But when that water finishes, well, there is unheated water for some moments.

It takes time to give warm water depending on the distance from the water heater to the shower.


No particular way to solve it. But you can skip showering before passing cold water.

The Air supply Is Blocked

When the air supply is blocked, you can see an error code on display. It means venting the problem.


Check out all vent pipes to connect correctly. Follow manual book instructions to meet the requirements.

Ignition Failure

The water heater fails to ignite due to many problems. But mainly gas supply problem helps to fail to ignite.


The gas valve should be opened fully and full the propane tank. If things don’t get sort out, try out technical support help.

Flame Failure

Gas pressure or electrical issue causes flame failure. Too small gas lines, regulator failure, venting issues, etc., can be the reason behind flame failure.


Check out little or simple reasons that cause flame failure. If it does not work, then taking technical support is better for you.


Why my tankless water heater is not supplying warm water?

Tankless heater heats and supplies water on demand in multiple appliances at the same time. It makes it difficult for the heater to warm water instantly. For some moments, you need to wait until the water gets warm.

How can I reset my tankless gas water heater?

The steps are as followed:

  • Click on the red reset button situated in the center of the control panel.
  • Press the button gently. Sometimes it becomes sticky.
  • Wait to hear a button click sound.

Can I increase the temperature on my tankless water heater?

Yes, you can control the temperature on your tankless water heater. There is a LED panel; here, you can set the temperature as you desire. It gives you a chance to set temperature degree by degree.


There is both a good and bad side to everything. The tankless water heater is not above it. There are a few troubles while using it. We just don’t calm down and try to find out the solution on the net by searching, “Why does my tankless hot water heater go cold?”

It has some solvable problems, which are mentioned and explained in detail above. They don’t make you suffer much. Because of its practical use and great service, people use it worldwide.

Ignoring minor problems, people are buying it instead of a water heater with a tank. It’s highly demanded in the market. It’s also affordable to limited-earning people. From my thought, I highly appreciate you buying and using a tankless water heater. Hope this “Why does my tankless water heater go cold” post is useful for you.

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