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! we are here to provide you with detailed tips and tricks on how to locate water leaks, 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
  • Temperature and 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


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.

Temperature and Pressure relief valve

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

When the water temperature inside the heater exceeds the set limit, the temperature sensor activates the TRV valve and releases a controlled amount of water to prevent overheating. Similarly, when the water gets heated due to thermal expansion, the pressure inside the heater exceeds the set limit, then the pressure sensor activates the PRV valve and releases pressure to prevent an explosion.

Related article: Tankless Water Heater Expansion Tank: A Must-Read Guide Before You Buy

pressure relief valve corroded or drain cap damaged

manual pressure relief values fixed on inlet and outlet pipes

When the TPR valve in your tankless water heater gets damaged or blocked, high temperatures and pressures are formed in the system, which can lead to leaks or even cause the whole system to malfunction. Also, check whether the rotating knob and drain cap are working fine. It is essential to have a professional plumber regularly check and test the valve to make sure it’s working correctly. If it’s not, it needs to be replaced right away 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. 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 water inside the unit. it’s recommended to have regular maintenance 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 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 down the road.

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 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.

Categorized in: