Why Does My Tankless Hot Water Heater Go Cold?

Why are tankless water heaters in so much demand lately? Tankless water heaters tend to have replaced traditional water heaters. Although they might use the same source of energy their mechanism of working is entirely different.

Have you ever gone for a hot shower and got cold water splashes in between? And it made you think that “Why does my tankless hot water heater go cold?” A tankless water heater does not store water rather it heats water on demand as it passes through the pipes.

This feature of a tankless water heater prevents energy loss and makes these units highly energy efficient. Being energy efficient they reduce the cost of your bills and are super affordable for daily use.

The list of pros of these tankless water heaters does not end with energy efficiency only. These units need less room than traditional water heaters which enables the buyer to install these units in compact spaces. Like any other unit, the tankless water heaters are not all perfect.

Sometimes issues may arise with your unit which is not frequent. To avoid these issues it’s important to install the unit properly with guidance from professionals. Make sure all the connections are tight and proper. The most frequent issue with tankless water heaters is improper heating.

This article explains the issues that cause cold water delivery at fixtures, their causes and possible ways to fix the problem. The most common query by most tankless water heater owners is that they don’t get instant hot water as they open the tap.

And this is because tankless water heaters are not instantaneous they have no hot water storage in fact the water gets heated after you open the tap and it starts flowing through pipes. So you need to be patient to get hot water from your tap. Some tankless water heaters now have a recirculation pump which makes them super fast in the delivery of hot water.

The good news is you can reset your tankless water heater anytime you want without going through the whole troubleshooting process.

Steps to Take to Avoid Tankless Water Heater Going Cold

After purchasing the tankless water heater for yourself keep in mind the things below to avoid any issues that may arise after installation.

1. Proper Installation

After buying a tankless water heater the first important task is to properly install the unit. If the process involves gas Piping then it’s recommended to take professional help. This lessens chances of error which will later cause inconvenience for you.

Make sure the size of the gas line is apt for the water demand so water will heat as required. Keep all the cold water line connections tight and appropriate. Improper installation will be leading to various issues in the future so make sure you have done it the right way.

If you want to do it all by yourself then get help from customer service with any queries you might have. Don’t experiment with the unit as it can lead you into serious trouble.

2. Gas Pipe Length

The length of the pipe affects the time it will take for the hot water to be delivered. Keeping the length of the pipes shorter will take less time to push away the cold water and hot water reaches fixtures earlier. It is thus normal for all tankless water heaters to take some time to deliver hot water through the fixture.

Some Other Common Water Heating Issues Can be

No Hot Water at All

You went to the kitchen to do dishes one night and all you get out of the kitchen tap is freezing cold water? You will be wondering what got wrong with the water heating unit. This occurs due to flame failure.

If no ignition is present at all the water won’t heat up. It’s a common problem with tank-less water heaters and if you face this issue check to make sure that the water, electricity, and gas supply to the unit are proper and not leaking or broken. Look for the shut-off valve and make sure it’s not closed.

Check the control panel of the unit to see is there any error code that might be hindering the heater from operating if this is the case reset the system to start the system running again.

Minimal Flow Rate

Ensure an appropriate flow rate through your tap. As the tap is turned on the water flow should be appropriate according to the needs of the water heater so the water heating system will work fine. Make sure the pipes are not blocked. Low water pressure will affect the working of the heating unit. If the water pressure is low then the temperature will fluctuate.

Frozen Pipes

This problem can occur during winter times when water in pipes gets frozen and so it takes longer than normal to get the required supply of hot water. When water solidifies inside pipes the heat is first used to melt it and then heat it so the resulting water temperature won’t be as expected.

It takes longer to get the hot water supply out of the tap when water is frozen inside pipes. This issue can be avoided by insulating all exposed pipes.

Water Heater Temperature Setting

What’s the right temperature for my unit? If you were pondering about this question then here’s the answer. Most manufacturers recommend keeping the temperature around 120 degrees Fahrenheit which is the default setting. The minimum temperature limit is 100 degrees Fahrenheit and the maximum limit for residential use is 140 degrees Fahrenheit.

You might have mistakenly set the temperature of the water heater too low. Raise the temperature to 125 degrees Fahrenheit or above when needed.

Water Filter

The water filter should be cleaned monthly so it won’t get clogged. If you don’t get hot water out of the tap at times of need then look for the cold water inlet into your system. At the end of this inlet, a filter is present that stops dirt and debris from reaching the heating system along with water.

With time the dirt can accumulate and clog the filter. This can be avoided by monthly cleaning the filter. If the filter is clogged then no water will go into the system and thus you will get a cold water supply.

Plumbing Crossover

This situation causes mixing of hot and cold water which results in a reduction of overall water temperature. To avoid this from happening you need to know how to test for plumbing crossover. Shut off the cold water supply to your water heater. Open all the taps. If after about 10 minutes of opening the tap water is still flowing out then you have a plumbing crossover.

Gas Valve Defect

If the gas valve is not providing the needed gas pressure then water won’t heat. Make sure the gas connections are done right and with the help of a professional technician. Check for any possible leakage.

Restricted Hot Water Supply

When the hot water out supply is restricted the temperature fluctuates. Check the shower heads and fixtures to make sure there is no blockage. If there is an excessive mineral deposit then replace the units with new ones. It’s advised to clean the fixtures from time to time and deposit them in vinegar for some time to dissolve the mineral buildup.

The latest tankless water heater models have an automatic bypass system equipped with a water adjustment valve. This advanced feature ensures water temperature stability and is consistent with the supply water temperature.

Heat Exchanger Sedimentation

If the sediments build up inside the heat exchanger they cause reduced transfer of heat. Descaling is important to remove all the mineral buildup and ensure the needed heat supply to the water running through pipes.

Monthly maintenance is important as it helps avoid excessive mineral build-up which after some time might be irremovable and thus you’ll have to buy new parts.

Cold Water Sandwich

This term signifies a situation when on opening the tap you do get the hot water but in between, you get an unwanted stream of cold water. This situation can be pretty uncomfortable for many. It might be the hot water remaining from the last time you used the tap.

The heater could not heat water super quick so the owner gets some cold water before the water is heated again. Unless some special features are installed in the unit to avoid this issue, this will occur with all tankless water heaters, especially the ones using electricity.

Error Codes

The control panel of the tankless water heater consists of an LCD screen and a microprocessor. This system displays an error code whenever a problem occurs. The error codes help the user understand what’s the cause and probable solution of the problem. The error codes are listed in the user manual or can be found even online.

Even getting help from a technician becomes easier cause they can look at the code and diagnose the defect. If the temperature fluctuation problem of your unit is complex hire a professional to help you out.

We hope this article was helpful for you to add to your knowledge that “Why does my tankless hot water heater go cold?. Do you have any confusion? Please comment below and we will discuss that with you.

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With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.