Top Tankless Water Heater Problems

image of homeowner taking shower and running out of hot water due to broken tankless water heater

Owning a house means dealing with one problem after another. Something is always breaking down from the plumbing to the heating system. The best way to handle these is to actively prevent them from happening in the first place. In order to do this, you must become aware of the common issues for every part of the house. Minor issues may be solved with simple solutions. Major problems will need the attention of an experienced professional. In this article, we focus on the top tankless water heater problems. This way, you will be able to perform some basic tankless water heater troubleshooting and understand the cause of your issue.

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Top Tankless Water Heater Problems

Keep reading to explore the most common problems with on-demand water heaters.

1. Tankless Water Heater Ignition Problem

image of homeowner troubleshooting a tankless water heater

If ignition can’t take place, then the water will not heat up. Instantaneous water heaters will flash an error message on the display to let people know what’s going on. This could happen because of a lack of fuel, a valve closure, an ignition pack failure, or other anomalies. Checking the gas supply and fuel valves may lead to a quick fix. Perhaps you are out of fuel and only need a propane delivery. Maybe you just have to open a valve. If the problem persists, then it’s time to call a plumber for assistance. There could be a deeper issue that requires parts replacement.

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2. Mineral Build-up In Your Tankless Water Heater

This is a common problem in areas with hard water. The large amount of minerals in the liquid can stick to the bottom of the heater and result in scaling. These are usually made up of calcium and magnesium. Finding another water source is next to impossible. Fortunately, homeowners can easily remedy the situation by flushing the system twice a year using a de-scaler cleaning kit. They can also use water softeners to minimize mineral build-up moving forward. Plumbers can provide other ideas that are tailored to specific situations.

3. Tankless Water Heater Flame Failure

image of a tankless water heater repair

This may seem like it’s the same thing as an ignition failure but the underlying causes are much different. In this situation, ignition occurs but the system cannot produce flames consistently. The culprit could be poor ventilation, a narrow gas line, or failed regulators. Those who are using propane should check whether there is fuel left in the tank. As for those using natural gas, see whether there is a supply issue with the utility company. Lastly, inspect the vents for any blockage. If all of these preliminary steps did not fix it, then the next course of action is to call for professional help.

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4. Erratic Temperature

It can get confusing when you experience an erratic water temperature while taking a shower. It may be hot one moment and cold the next before getting hot again. This usually happens when a person showers after someone has just used the tankless hot water heater. This “cold water sandwich” only happens in the first few moments. If you start immediately after the last person, then you will get the leftover hot water from the previous shower session. However, the heater might have switched off in the meantime so that will be followed by cold water. Once the heater switches on, the water will get warm again. The system is actually working as designed. There is no fix aside from having the patience to let water flow a bit before moving under the shower.


5. Tankless Water Heater System Overload

Aside from the shower, the tankless water heater may be connected to the taps around the house. If people are using many of these at the same time, then the heater may shut down due to a system overload. This means that it has exceeded its capacity. Therefore, the solution is to reduce the simultaneous demand for hot water. If this feels inefficient, then consider upgrading to a higher-capacity water heater. It may also be possible to get a second heating unit to double capacity. Talk to a plumber for advice on the right course of action.

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6. On-Demand Water Heater Airflow Issue

The display may show an error message that points to a blocked air supply. This is the system’s way of indicating a problem with blocked vents. It could also be an issue with combustion due to poor airflow. The first response should be to inspect the vents and remove any obstructions found around them. Then move on to the vent pipes to see whether they have gotten loose or disconnected somehow. You may also get help from the plumber to plug leaks and fix any mistakes with the installation of the unit.

7. Minimum Flow Rate Of Your Tankless Water Heater

Sometimes the shower seems to be working fine only for the water heater to shut off abruptly. When this happens, the person will feel an unwelcome rush of cold water. Fortunately, this no longer happens much with newer models. Older ones are prone to it due to their design, especially when paired with a water-saving showerhead. This combination may push the flow rate below the minimum system requirement to fire up the heater. It is a complex problem that calls for the expertise of an experienced plumber.



Regular maintenance is the key to stress-free homeownership. Schedule periodic inspection and cleaning of every appliance, including the tankless water heater. Seek out the help of a plumber if you encounter problems that need advanced solutions.

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Contact Robinson Plumbing, one of the most trusted plumbing companies in the Lehigh Valley, for reliable plumbing services. We offer various plumbing services ranging from tankless water heater repair, drain clogs, water heater replacements, toilet repairs, water leaks, and more. We always give a wide range of solutions when possible for any plumbing repairs. This allows you to choose the best options for your home and budget.

Find yourself dealing with an unexpected plumbing problem in the middle of the night? No worries! You can count on the expert plumbers at Robinson Plumbing to take care of you. We offer reliable 24-hour emergency plumbing services. You can count on us to get the job done quickly and correctly and, best of all, at an affordable price.

We proudly offer the most affordable and best plumbing services in the Lehigh Valley area. Our plumbers all have the proper licenses and expertise to ensure your satisfaction. All of our work comes with a guarantee. Contact Robinson Plumbing today and schedule your free estimate.

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