5 Common Issues with Tankless Hot Water Heaters and What to Do About Them

December 26, 2019

Installing a tankless hot water heater is a great way to improve your home’s energy efficiency and streamline your maintenance budget. They’re durable, last for well over 20 years with regular care, and use less energy to keep your home supplied with hot water. Though they’re durable, tankless water heaters can have a few unique problems that other systems don’t. Your Denver plumbing team wants to help you keep your unit working flawlessly. Here are a few of the most common tankless water heater issues and what you can do to fix them.

The Heater Won’t Turn On
Tankless water heaters provide hot water on-demand. But sometimes, you’ll notice that the water just won’t get hot no matter how long you leave the tap running. When this happens, you likely have an issue with the fuel source. If the water heater can’t get fuel, it can’t ignite and warm your water up. 

If you have an electric tankless water heater, check your breaker box. It’s likely that you blew a fuse on the outlet. If you have a gas water heater, make sure the gas supply is turned on for the water heater. If everything looks like it’s supposed to, call your plumber and let them inspect the unit. 

The Tap Changes from Hot to Cold 
Tankless heaters, like standard units, need a little time to heat the water. Once the water gets up to temperature, it stays that way until you turn the tap off. When the tap turns off, it stops heating the water up until you turn it back on. 

If you have hot water that flashes cold for a few seconds, it’s likely not an issue with your water heater—it’s a problem with the way you’re using it. Remember, the heater stops heating the water once the tap turns off. This means if another person showers before you do, the water heater will need a few seconds to reignite. The initial burst of hot water you feel is what gets left in the lines. Once it’s depleted, you get a few seconds of cold water while the water heater ignites. 

In most cases, this will happen just once or twice while the unit is warming up. The best thing you can do is let the tap run for a few seconds before you start using the hot water. This will help you avoid discomfort. However, if you notice the temperature changes happening throughout your shower or happening when the tap hasn’t been used by someone else, call your plumber.

The Water Heater Tells You the Exhaust is Blocked
Most tankless systems are designed to make it easy to troubleshoot issues. When something is wrong with the system, the display will at least give you an idea of what’s going on. For most homeowners, the first and most common error message they’ll see is a blocked exhaust notification.

Tankless systems need access to fresh air anytime they’re running. They also need to be able to vent to the outdoors when they’re actively heating the water. If the exhaust is blocked, they can’t get the air they need to maintain the heat. 

If you’re getting an error message about the exhaust, make sure the channel is open. By the water heater, check for dust bunnies and objects that could be blocking the vent. Outside your house, make sure any openings are free and clear of debris. If you can’t find anything blocking the vents, schedule an inspection with your plumber. 

There’s Something Growing in the Unit
When you turn on the tap, you expect to see clear and clean water every time. You know what it’s supposed to smell like and can tell if something’s not right. If you notice discoloration or a strange smell anytime you turn on the hot tap, you likely have something growing inside your tankless hot water heater.

Though this sounds serious, it’s not as big of an issue as you might think. Tankless systems are exposed to the minerals in your tap water at all times. As you use the heater, the minerals can start to build up inside the lines and system. Once the minerals build up enough, it may cause the water to start to smell when the tap is on and can leave it looking cloudy, yellow, or even brown. 

All you have to do is flush your tankless hot water heater with vinegar or a descaling solution. If you’re not sure how to flush your unit, get your plumber to walk you through the process. Ideally, you should flush the system once every six months to keep buildup from happening in the first place. Even better, doing so will extend the life of the unit and will keep you well-supplied with hot water whenever you need it.

The System Is Overloaded
Tankless systems work best when you’re only using one or two hot water taps at any given time. This ensures that the system can produce enough hot water for your family to use without getting overloaded. But what happens if multiple people are showering, another is doing a load of laundry, and another is washing dishes? The system could stop working altogether.

This happens anytime the water heater is overloaded and can’t keep up with demand. If you’re running into this problem almost daily, you likely need a larger or a second unit. But if it only happens occasionally, just turn one of the taps off and let the unit recover. If it still won’t reset itself, you may need to manually reset the system. Remember, it doesn’t mean anything is broken or that the unit isn’t working…it just needs to restart and recover.

When In Doubt, Call Your Plumber
Tankless hot water heaters are great, but they’re not infallible. If you’re ever unsure about what’s happening with your unit or just want a second opinion to make sure it’s working properly, contact our team as soon as possible. We’ll make sure your water heater can keep up with your demands easily. 
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