Tankless water heaters are known for being efficient and space-saving, but like any home system, they can still run into problems. While these work differently from tanked models, the issues they face are usually easy to understand once you know what to look for.
Heat Exchanger Problem
When your tankless water heater works as it should, you get hot water fast, and it stays hot. But something isn’t right if your shower turns cold halfway through or the water temperature jumps around while you’re washing dishes.
One possible reason for this issue is that your unit struggles to keep up with demand. If someone’s doing laundry while you’re using the sink or shower, that can affect the flow. Tankless systems heat water as it passes through, so if more than one person uses hot water simultaneously, it might hit its capacity.
However, there is also a chance the heat exchanger isn’t working properly. If the issue is not related to multiple household members using hot water at the same time, you will need to contact us to inspect your system. The problem could be related to debris buildup, electrical or fuel line trouble, or a faulty heat exchanger.
No Hot Water
You may turn on the tap expecting a strong stream of hot water, but you get cold or lukewarm water instead. If the cold water flows normally but the hot side drops off significantly, your tankless water heater is the source of the problem rather than your plumbing. These systems require a minimum flow rate to activate the burner or heating element, depending on whether your unit runs on gas or electricity.
If the water moving through the unit doesn’t meet that threshold, the heater won’t produce hot water even if you leave the tap running. One common cause is mineral buildup. Hard water can leave calcium and magnesium deposits that accumulate inside the unit. This usually happens near the inlet filter or within the heat exchanger. Over time, this buildup restricts the water flow. Even if it doesn’t cause a full blockage, the reduced flow can prevent the unit from turning on consistently.
In other cases, lack of hot water may stem from recent plumbing changes. For instance, if you’ve recently installed a water-saving fixture, the system may not detect enough flow to trigger heating. This is particularly common with low-flow showerheads or new faucet aerators that reduce water consumption but unintentionally interfere with tankless heater activation.
If you’re experiencing this issue, a professional inspection is your next step. Our technician can check for internal scaling, clean the inlet filter, and evaluate whether plumbing modifications are affecting the heater’s performance. Cleaning or a minor adjustment can often resolve the problem.
The System Shuts Off Without Warning
If your tankless water heater powers off suddenly while you’re using hot water, it’s a sign that something is wrong. Most tankless systems have safety features designed to shut down the unit automatically to prevent internal damage.
One common cause is overheating due to poor ventilation. Tankless water heaters generate significant heat as they operate and rely on a properly sized and unobstructed venting system to expel that heat and exhaust gases. If the vent is too small, incorrectly installed, or blocked by debris, the heat and exhaust can build up inside the unit. When internal temperatures rise beyond safe operating limits, the sensors inside the heater trigger an automatic shutdown to prevent a fire hazard or component failure.
Another possibility is a faulty sensor or control board issue. Tankless units have several safety sensors that monitor temperature, pressure, and airflow. If any of these sensors malfunction or misread data, the unit may shut down even if the actual conditions are within safe limits.
You may not always see an error message on the control panel, but most models store error codes internally. One of our technicians can retrieve those codes and use them to pinpoint the root cause of the issue.
For homeowners, these types of shutdowns aren’t just frustrating. They can also signal developing problems that should be addressed promptly. If your unit frequently turns off while using hot water, it’s best to have us inspect the venting, sensors, and overall system to ensure everything is operating safely.
An Increase in Monthly Bills
If your home has hard water, your tankless heater will likely experience scaling problems. Hard water minerals can gunk up the inside of your unit, especially around the heat exchanger, where the water gets hottest.
As the buildup grows, it acts like a layer of insulation between the water and the heating surface. That forces the unit to work harder to reach your set temperature. You may still get hot water, but the unit takes more energy to produce it, and it might not last as long during use.
You might also hear strange noises coming from inside the unit. A popping or crackling sound can mean scale buildup and uneven heating. Some systems have alerts that remind you when it’s time to flush the unit, but not all do. As part of annual maintenance, our technician will flush your heater with a descaling solution, which usually prevents scale buildup from becoming an issue.
Unit Is Too Small for Your Household
If your tankless water heater struggles to keep up with daily demands, it may not be due to a malfunction. Instead, the unit might not have been properly sized for your household’s needs from the start.
Tankless systems are rated based on flow rate (measured in gallons per minute) and temperature rise (how much the system can heat incoming water). A unit that’s too small won’t be able to deliver enough hot water when several fixtures are in use at the same time, such as during peak hours, like when everyone is getting ready for school or work. In practical terms, that might look like one person enjoying a hot shower while another gets only lukewarm water in the kitchen or, worse, no hot water at all.
This problem is especially common in homes with multiple bathrooms, high-flow fixtures like rain-style showerheads, or deep soaking tubs that require a lot of hot water in a short amount of time. Even energy-efficient or water-saving fixtures can become a problem if the total demand exceeds the heater’s capacity.
One of our technicians can evaluate your household’s hot water use patterns, number of fixtures, and peak demand to determine whether your current unit is the right size. If it’s not, they may recommend upgrading to a higher-capacity model or installing a second unit.
Contact Your Local Professionals
Just because the water heater in your Shreveport, LA home is compact and high-tech doesn’t mean it won’t need attention now and then. If your tankless system isn’t working like it should, schedule a visit with Bobby L. Greene Plumbing, Heating & Cooling Co. to get it running again. You can also count on us for plumbing repair, drain cleaning, and water treatment services.
