Welcome to WaterIIT
Your Ultimate Guide to Pure, Safe and Clean Water
Welcome to WaterIIT
Educate and empower to make informed decisions about water filtration needs
Welcome to WaterIIT
Our blog features informative articles, how-to guides, and product reviews to stay up-to-date on the latest trends and developments in the industry

Why Does My Tankless Hot Water Heater Go Cold?

A tankless hot water heater is a type of water heater that heats water on demand. This means it can heat up more quickly than a traditional tank-style system, but it has the potential for leaks and problems that can cause the temperature to go down or not heat up at all. If you’re having problems with your tankless hot water heater, there are a few common reasons why it may be going cold.

A tankless hot water heater is a good thing to have because it saves space and money. It does not need a tank for hot water storage, which means that it uses less energy than traditional heaters. However, there are some things that can cause a tankless heater to go cold.

The design of a tankless water heater was created to make life easier. However, there are some problems with this type of system that people should be aware of before purchasing one. The most common issue is when the temperature sensor goes out or stops working. This causes the unit to shut off and not produce any hot water until it has been repaired or replaced by an authorized service technician.

The tankless water heater is a great investment with many benefits, but one of the biggest gripes is that it can go cold. The reason why this happens may be due to some simple fixes on your part or there are other possible reasons for this situation. A common cause could be low pressure in the home; however, you should also consider how often you use hot water and what type of system has been installed on your property.

In this article, you will discover why your tankless hot water heater goes from hot to cold and how to fix the problem.

How a Tankless Water Heater Works

It helps to have a basic grasp of how tankless water heaters function to understand why yours would go cold on occasion. Tank water heaters are probably nothing new to you. Heaters that heat and store water have been around for a long time. The typical tank water heater in a home has a capacity of 30-50 gallons. That explains their enormous size!

Tank water heaters, as you might expect, waste energy by heating water that doesn’t need to be heated. Standby energy losses can have a significant impact on your monthly energy costs.

On the other side, tankless water heaters preserve energy while also saving you money. Tankless water heaters are compact since they don’t have a storage tank and instead heat water as it is needed.

The hot water is only available when you need it, similar to having “on-demand” hot water at your fingertips when you need it. Your tankless system’s flame ignites the heat exchanger when you turn on the hot water faucet. After that, cold water enters your water heater through an entrance pipe at the base.

The water circulates through the device, picking up any stray or “secondary” heat that may be present. Your tankless water heater system achieves the correct temperature by first passing the water through a main stainless steel heat exchanger. The tankless system’s hot water is now ready to be delivered throughout the home’s plumbing.

Why does my tankless hot water heater go cold?

Why is your tankless water heater not staying hot? A tankless hot water heater does not store water, rather it heats on demand. This means that if you have a cold shower or take a long hot shower, the water in your tank will go unused and the heating element will turn off until it’s needed again. If there is no demand for heat, then the system turns itself off to save energy and money.

It has been observed that some people have experienced their systems going cold due to several factors including clogged filters and deposits on heating elements or lack of insulation around them.

If you notice that your tankless hot water heater is delivering cold water, there are many possible causes and ways to fix the problem. The primary cause of this issue could be a clogged shutoff valve or insulation damage in the pipes leading from your furnace because it can’t regulate temperature as well.

The most frequent issue with tankless water heaters is improper heating. It’s important to make sure that the hot water heater achieves its full output, so it doesn’t go cold. If you’re having any issues with your unit, please contact our customer support team for troubleshooting help and assistance!

It’s not uncommon for issues to arise with tankless hot water heaters. Another of the most common issues is that they will go cold, which can be caused by a variety of factors. Sometimes these problems are due to faulty installation or damage from falls or spills; however, other times there may be more significant causes like electrical power outages and low-flow devices on your plumbing system.

If you want to prevent future issues with your service due to not having enough heat delivered at fixtures throughout the home, make sure all pipe insulation has been replaced and check for any debris buildup on faucets or valves.

One of the best ways to avoid this problem is by installing a thermostat on your tankless hot water heater so that it can turn itself on when needed.

In a tankless hot water heater, the energy efficiency is superior to traditional models because of no energy loss through pipes.

If your tankless hot water heater is acting up, you can reset it in a snap. All the user needs to do is turn on their cold water tap and hold down the button for at least 10 seconds before releasing it. This will cause the system to restart with no loss of functionality or energy use over time.

Reasons your Tankless Hot Water Heaters go Cold Sometimes

A lot of people ask why their tankless hot water heater goes cold when they turn it on and this question may become more common as the weather gets colder. Here are the reasons why your tankless water heater water goes from hot to cold.

Improper gas line size

An undersized gas line can cause equipment failure. If you are experiencing problems with your tankless hot water heater, it may be due to an undersized gas line.

Furthermore, Rinnai Tankless Water Heaters are only compatible with natural gas or liquid propane. If you have a home that uses different types of fuel for heating, it is important to find out which type the water heater will use before purchasing one.

Dirty filter on the cold water inlet

The most common reasons tankless hot water heaters go cold are when the filter is clogged or not performing. Make sure that there isn’t debris in the cold water inlet before you turn it back on.

In order to prevent a filter from getting clogged in the long run, it is important to regularly clean it. The best way would be to use a vacuum cleaner or dishwasher for this purpose.

Clogged heat exchanger

A clogged heat exchanger is one of the most common causes of cold water in a tankless hot water heater. Mineral build-up can be prevented with regular maintenance and cleaning, or by using a salt-free solution to wash the unit’s heating element.

Limescale is a mineral deposit that builds up in an appliance’s heat exchanger, such as a water heater. It can cause the temperature to fluctuate and affect performance.


The temperature of the water heated by the heating element is controlled by thermostats attached to the top and lower heating elements. Even while thermostats don’t go down as often as heating components, they still need to be checked if your system stops generating hot water.

Low Water Pressure

If the water pressure is low, then it can be hard to maintain a constant temperature. Gas burners should be turned off before turning the hot water heater off.

Low water pressure is when the flow rate of a faucet or showerhead falls below its activation flow rate. This can cause some issues such as low-pressure washing and leaks in appliances.

The water pressure in a tankless heater is controlled by the size of the pump. The bigger it is, the greater its ability to move water from one point to another and produce hot or cold temperatures based on user settings. In order for this system to work properly, only certain models are able to withstand high amounts of power consumption without compromising performance.

When installing a tankless water heater, you must ensure that there is enough proper gas pressure coming in to turn on your system. Check all of its sensors, wiring fuses, and components before making any repairs or replacing them because they could be burnt out.

Plumbing Crossover

A single-lever faucet is not designed to work with a hot and cold water line. When the hot water is turned on, it will drain out of the cold side. The solution to this problem would be replacing or repairing the plumbing crossover that connects both lines together

If your water temperature fluctuates from hot to cold or if you have a single-lever faucet and the washer has failed, contact a local professional today.

Cold Water Sandwich

A tankless water heater is a device that makes hot water from cold water. It takes little time to heat the cold water, so it will get too cold and stop working. The most common reason why your tankless hot water heater stops heating up is that you have not run enough hot tap for long enough time or there has been a power outage in your area.

The tankless water heaters will gradually heat the cold water. The time it takes for the hot water to reach 100 degrees Fahrenheit in about 4 seconds. Sometimes your hot water heater will go cold before the tank starts heating again. One of these reasons could be that there’s an air leak or that something has blocked it from running properly.

A tankless water heater could go cold when there is a leak in the system. This can be inconvenient as it means you cannot use hot water for showers and other purposes.

Why does my Rinnai tankless water heater go cold after a few minutes?

There are a number of reasons why your Rinnai Tankless Water Heater isn’t working properly, the most common of which being incorrect installation or maintenance. But don’t let that get you down. It’s easy to take care of cold water sandwiches and filthy water filters on your own.

It’s possible that a plumber is required, though, when dealing with a defective heating element or an inadequate gas line. Check your system’s error codes to see if there are any additional surprises there, too. If you aren’t sure what to do, contact a local professional today.

Ways To Keep Your Tankless Water Heater Warm All Day

Hard water may block pipes and cause corrosion because it creates a hard scale inside of them. As well as fixing this issue, installing a water softener might enhance your quality of life by enhancing the refreshingness of your shower and bath as well.

It could even improve the flavor of your drinking water as well as extend the life of your laundry. Using your tankless water heater after a mineral building has already happened will require the services of a professional to remove the accumulation.

To avoid the accumulation of calcified mineral debris in the water heater’s tank, it should be cleaned out regularly. Buying a tankless water heater might help you prevent a lot of difficulties in the future. When you require hot water, tankless water heaters simply heat the water that is flowing through them; they turn off when no longer needed.

Another approach to improve the efficiency of your water heater is to flush it thoroughly. In general, manufacturers advise customers to perform this task twice a year.

Consult your owner’s handbook carefully before flushing it out. Using a hose connected to a drain valve located someplace outside your home, such as an open storm drain, will allow you to remove the waste without damaging your property.

What is a cold water sandwich effect?

If you have a tankless hot water heater, it can take a while for the water to heat up. This is because the water that flows through the unit has to be heated before it can flow through it. The cold sandwich effect happens when there isn’t enough time for the hot water in your tankless system to warm up, so some of it will stay cold and some will go out as steam or not at all.

A “cold water sandwich effect” is when some of the hot water in a tankless system gets trapped and turns cold before it can be used. This “sandwich” of cold water may happen when the tankless system doesn’t have enough time to heat up the water.

This happens because there is a time delay between the tankless water heating up and coming out of the tap. It’s not always an easy thing to keep your hot water at the right temperature, but there are a few things you can do to try and prevent the cold water sandwich effect.

  • Take shorter showers
  • Keep your tankless system clean by blowing it out once a month
  • Be careful not to mess with the temperature dial on your tankless water heater
  • Avoid using hot water for things like washing dishes or brushing teeth
  • Try to limit the number of people using hot water in your house at one time

Hi Guys, Mike is a Mechanical Engineer who specializes in Heating, Ventilation, and Air-conditioning. His love for humanity and his profession propels him to share useful and factual Information on this blog.

Wateriit.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

Leave a Comment

Wateriit.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

Recent Posts of Water Filters

Recent Posts of Water Heaters

Recent Posts of Water Softeners

Recent Posts of Water Treatment

Recent Posts of Water Purification