Tankless water heater leaking? find and stop the leak

Is your tankless water heater leaking? Learn where to check for leaks, reasons why leaks occur and how to fix them.


Life is going on smoothly with hot showers on cool days with your tankless water heater which you bought for an instant and unlimited hot water supply. But suddenly one morning you noticed water leaking from it and don’t know what to do. Don’t panic! Our HVAC Expert Joseph is here to provide you with detailed tips and tricks on how to locate water leaks in tankless water heaters, what causes the water leaks, and how to fix those leaks.

The first step to perform as soon as you see the water leak from the heater is to turn off the power supply to it. If your heater is connected directly, turn down the circuit breaker. Do not go near and do not touch the heater till you cut the power to it. As water is a good conductor of electricity, you may get an electric shock if you do so.

Reasons why a tankless water heater leak

There are several reasons why a tankless water heater may start to leak, they are listed below.

  • Clogs
  • Corrosion
  • Pressure relief valve
  • Inlet and outlet connections
  • Old age

Clogs caused due to hard water

Clogs in a tankless water heater can occur in various parts of the system like water inlet and outlet connections or pipes, valves that control the water flow, or in the heat exchanger itself. These clogs are caused due to the mineral buildup from the hard water scales when it is heated, not only scales but also caused by debris, like sand, rust, and sediment that enters the system.

lime scales in pipes and hoses of tankless water heater

When these clogs form in the system, they can reduce the water flow rate through the system. If you stay in the US, the lime scales formed from the hard water contain high amounts of minerals like calcium and magnesium which attaches to metal components like pipes and heat exchanger which blocks the water flow and slowly corrodes them.

concentration of hardwater in united states chart map

The above image represents the hard water of water in different locations in the United States. National Water-Quality Assessment (NAWQA) conducted water condition tests in 2100 wells across the US and the results are shown on the map.

Prevention Tip:

To prevent clogs in a tankless water heater, it is important to perform regular maintenance by a qualified plumber. This can include flushing, descaling, and cleaning the heat exchanger, water inlet and outlet connections, and pipes. We can also install a water softener and sediment filter to reduce the amount of minerals entering the system, and remove debris respectively.

Also read: How to reset a tankless water heater

Leaks caused due to Corrosion of metals

Corrosion is the gradual destruction of materials (usually metals) by chemical reactions with their environment. It can occur in tankless water heaters due to exposure to water and other substances over time and can lead to leaks and other issues.

corrosion in metal pipes and parts of tankless water heater

As tankless heaters heat water at high temperatures some minerals or chemicals present in water react with metallic components in contact which make them corrode and gradually build small holes through which water leaks out.

Leaking from Pressure relief valve

A pressure relief valve (PR valve) is a safety device that is installed on a tankless water heater to prevent dangerous buildups of pressure inside the unit. Some units have different release valves for pressure. These valves are designed to open and release water or pressure if the pressure inside the tankless water heater becomes higher than the set limit.

When the pressure inside the heater exceeds PR valve and releases a controlled amount of water or air to prevent overpressure in the unit. Over pressure in the unit causes damage to the pipes, fittings or even an explosion.

pressure relief valve corroded or drain cap damaged
manual pressure relief values fixed on inlet and outlet pipes

When the PR valve in your tankless water heater gets damaged due to corrosion or physical damage can lead to leaks. Also, check whether the rotating knob and drain cap are working fine if it gets damaged water drips through it. It is essential to regularly check and test the valve to make sure it’s working correctly. If it’s not, it needs to be replaced to keep your tankless water heater running safely and efficiently.

Inlet and Outlet connections

The inlet and outlet connections on a tankless water heater are like the pipes or hoses that bring in the cold water and take out the hot water. They’re usually found on the bottom of the unit and can be made of metal, plastic, or a combination of both.

As time goes by, these connections can become loose or damaged due to regular wear and tear, corrosion, or poor installation near fittings. This can cause water to leak from bottom of heater. If the same thing happens with the outlet connections, hot water leaks and reduces the hot water flow to the fixtures or appliances.

To avoid these types of leaks it is important to inspect and tighten or replace these connections with new and good-quality pipes or hoses.

Additionally, proper venting should be done to avoid the heat vapors condensing inside the unit by creating water droplets. Joseph recommends you to spends some time to have regular checks to detect any signs of blocks or wear and tear to address any issues promptly.

Old age

As a tankless water heater gets older, its internal parts can start to deteriorate and lose efficiency, causing increased wear and tear on the system. This can lead to higher energy bills and a decrease in hot water flow and temperature.

Over time, important parts like the heat exchanger, burners, and control valves can become corroded, damaged, or worn out. This can cause leaks or the whole system to malfunction. Additionally, the seals and gaskets that prevent water leaks can become hard and worn, resulting in actual leaks. It’s important to keep an eye on these internal components and address any issues promptly, to avoid bigger problems in your water heater.

How to locate water leaks in a tankless water heater

After cutting the power supply look at where the water is leaking, either it’s leaking from the bottom of the unit where the fittings are there or from inside the body unit.

If you see clearly that water sprinkling from the pipes or hoses near the bottom fittings and not from inside the heater body, then it is easy to solve the issue. To do so first close the water supply and replace or repair the pipes or hoses which are damaged can solve the issue. Sometimes threads between fittings go wrong, which can be solved by using sealant tape.

But if you see water leaking from inside the unit, it may be serious. There can be multiple reasons behind it. Open the front panel of the unit and check from where the water is leaking. If the water is leaking near any valves check for damages and try to repair or replace them. If the leaks or from the Heat exchanger, consult an experienced technician or plumber because we cannot fix it by ourselves easily.

Frequently asked questions

  • What to do when your tankless hot water heater leaks?

Shut down the power supply, and inspect the leaks, if it’s a minor leak follow the above steps to solve them. if you cannot, then consult a professional plumber or technician for support. Ask them the reason why it happened and tips to prevent it happen again in the future.

  • Plumber recommends a safety device, should I accept it?

First, ask for the reason why it needs to be installed. If you feel legit then agree, adding safety to your system is good for the long run without causing major repairs.

If you have any questions or concerns, don’t hesitate to leave a comment below! Our team is here to assist you and provide all the information you need. Your feedback is important to us, so please feel free to share your thoughts and we’ll respond as soon as possible.

Joseph Miller

Joseph Miller is a highly experienced water heater repair expert with a passion for keeping homes warm and comfortable. With over 50 years of industry expertise, Joseph has developed a deep understanding of water heater systems and the intricacies of their repair and maintenance.

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  1. Investing in maintaining your water heaters to prevent leaks from damaging your home makes sense. I have a friend who wants to invest in keeping his property warm during winter. I should talk to him about finding a water heater supplier that can help him install and maintain these units in the future.

  2. It’s interesting to learn that water heaters could start leaking for different reasons, but they must be inspected as soon as you identify a leak. My mom called me earlier and mentioned that she found a pool of water under her water heater. I think her unit is too old to be working anymore, so I’ll suggest we look for a plumber tomorrow to inspect her water heater.

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