Common Tankless Water Heater Problems And How to Fix Them

With the advancement in technology, more focus is put on designing energy-efficient tankless water heaters so that the consumers face low tankless water heater problems and also have lesser harmful effects on the environment.

Tankless water heaters heat the water when the tap is turned on. The faucet when turned on water flows through the pipes and the heating coil runs either using gas or electricity heats the water.

The water is heated on demand so there is no heat loss. Problems can arise in any unit if the connections are not done properly.

In this article, we will look into detail about the most common problems faced by the owners of electric and gas tankless water heaters and how to solve them.

Gas vs electric tankless water heaters is a common discussion. Both have their pros and cons. Here we will look for some common issues you can face with both types of units.

Tankless Water Heater Problems

Let’s discuss the common problems that the users face with their tankless water heaters. We will be going through the issues of both Electric and Gas tankless water heaters.

Electric Tankless Water Heater Problems

Have you ever stepped into the shower for a hot bath and instead got splashes of cold water? This happens due to some sort of issue with your water heater.

What might cause this issue? The answer is a long list which we will look into next. The first step for troubleshooting is to open the unit and look for faults in it. Before you do so don’t forget to disconnect the electric supply to the unit.

Forgetting to do so can have serious implications. Now we will go through all possible problems that might be affecting your hot water supply.

No Hot Water Supply

Sometimes it may occur that the water heater is not working at all so you just get cold water out of all faucets. This complete absence of hot water can be caused by a plugged heat exchanger due to the hard water supply.

This plugging is avoided by regular flushing. Blockage of vent causes the system to shut down and so there will be no hot water supply.

For gas, tankless water heaters ensure that your water heating unit has the right amount of power supply. If the supply is short of need then issues will arise with water heating. A dirty burner or bad ignitor both cause the heating process to stop.

This problem can be fixed by reducing water usage. Try to limit yourself to using one water faucet at a time. If doing so solves the issue it means that the problem is with the demand and not with the unit. And if you want to get a unit that will match the increased demand then get one with a higher flow rate.

If you are using just one faucet at a time and still this issue persists then make sure the gas supply is uninterrupted if the unit is being run on gas. Check the venting pipes are not blocked. Check the gas valve is turned on not off. Try giving the unit regular maintenance. This avoids a lot of problems and helps the unit function optimally for longer.

Inadequate Hot Water Supply

The hot water supply is not enough for all the house chores. This issue arises if you purchased a smaller unit that is not able to meet your demands. Try purchasing units according to the family’s needs so you will always have plenty of hot water available.

Tankless water heaters heat water on demand so don’t worry much. Because there is no reserve in a tankless water heater so it will take longer for water to heat than a normal water heater. In beginning, this long wait might be frustrating for you but you will get used to it with time.


If your water demand is 35 gallons buy a 45-gallon capacity unit. Even if the water demand outpaces capacity then take steps to limit use. Shorten the length of your showers. Install lower showerheads and try doing water-consuming activities at different times of the day so your water heating unit won’t be overburdened.

If the water supply has suddenly reduced from normal then your heating element has gone out of function for sure.

Too Hot Water Supply

Water temperature above normal can harm the skin. The skin gets burnt if the water temperature is not right. This situation might be frustrating for the user and occurs due to a defect with the thermostat. High temperature means the thermostat is set too high. You can adjust it back to normal yourself without any help.

Sometimes the problem is with the thermostat sensors. They have become loose. Adjust the thermostat and clean up the shower head if it solves the issue then the problem was with the thermostat setting. If the problem persists look for sensors.


Break the electric power supply to your water heater. Uncover the heating elements. Look for the thermostat temperature setting on both the thermostat. Make sure it’s within the normal range. The recommended limit is between 110 to 125 degrees.

Take a tool such as a flat head screwdriver to adjust the temperature to the desired limit. Bring the other thermostat to the same setting. Replace the insulation and plastic safety guard and reconnect the electric power supply. Wait for some time and the hot water supply is ready for use.

Why does my electric tankless water heater keep shutting off?

A water heater that keeps shutting off now and then will be surely very annoying. What causes this issue might not be a simple cause. We will list the most common ones here.

  • A loose wire can cause this issue for sure. If you suspect some problem with the wire connections then call in a plumber so he can fix it in no time.
  • Make sure your heater has the right supply of water gas and electricity.
  • Check your water heater filter to look for any trapped debris.
  • Make sure the water flow rate is right. Tank-less water heaters have a minimum water flow rate requirement and if the requirement is not met then the heater won’t turn on.

Water Leakage

Valves and connections might leak. Reasons can be diverse. Leaking water causes damage to the unit and is a hazard for the whole house. Sometimes water leakage is caused by loose connections if this is the cause of the problem in your case then tighten the connections.

Other times this happens due to corroded pipes. The corrosion of the pipes is caused by mineral buildup. The mineral build-up corrodes the pipes and creates holes that cause leakage. The solution for this is to replace the corroded pipe.

The corrosion can be prevented by cleaning the unit more often. If you have a hot water supply then installing a water softening unit also lessens chances of damage to the unit.


After long use, the pipes might corrode and this will cause water to leak out of them. Check that your connections are tight and not leaking. If you feel they have become loose then tighten them using a wrench. If your pipes have corroded then replace them with new ones as they can’t be repaired. To do so first stop off the water supply valve then replace the pipes.

Rusty Odor Water

The water coming out of your pipes should be clean and odour-free. But if you see some tint then it’s a sign that your pipes are rusting. Smelly water indicates the growth of bacteria and so is a sign that there is an immediate need for the replacement of anode rod. This repair requires professional help.

Noisy Water Heating

Does your water heater make an unpleasant sound as it heats the water? It’s surely due to sediment build-up in your tank. The sediment buildup needs to be removed. First, empty the tank and then clean it up. To avoid the build-up of minerals in your water heater do the monthly maintenance.

Mineral build-ups if not removed on time then can cause irreparable damage to your unit. This damage might arise a need for replacing the damaged parts. Even a warranty won’t be useful in this case cause it indicates your negligence.

Coldwater Sandwich

This is a pretty common and irritating issue faced with all tankless water heaters. This means as you turn on the faucet the water supply is initially hot then becomes cold and hot than hot again. The best possible solution for this is to install a recirculating system. Doing so will divert the water back to the heater. One solution is to replace your water heater cause this issue occurs more with the old water heaters.

Exhaust Problems

Tank-less water heaters have an LCD panel that shows error codes whenever any issue arises with your water heater. The code explains the cause and possible solution to the problem.

If your exhaust is blocked then the display panel will show an error code that will tell about the problem. This means the unit has a problem with venting.

First, check all the pipes for any holes. Make sure that you have installed the unit right according to guidelines. If the water heater is installed too near to other units it will block the air supply and create a fire hazard.

Vents outside the home might be blocked by bird nests to make sure all the vents are clear and fit for use.


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Gas Tankless Water Heater Problems

Ignition Failure

Failing to light up the water heater? This may be due to an empty propane tank. Make sure the gas supply is enough for use. If the gas valve is not fully open then the heating element will have less than needed gas supply. This will make water heat less efficiently. Open the valve fully. If doing so does not solve the problem then the issue is bigger and calls for a need of professional help.

Flame Failure

This can happen if either the gas supply or the electric power source is not working properly. First, make sure the propane tank is full yet. This issue can arise if the gas pipe is too short or there is a problem with combustion or venting pipes. If you are not able to understand the problem then take help from some professional to ensure the unit is repaired to its best form.

Why does my gas tankless water heater keep shutting off?

Just like the electric ones if the gas tankless water heater keeps shutting off then it’s too due to multiple reasons.

Defective Gas Valve

If the gas valve is interrupting the gas supply then the water heater won’t ignite and so the water will not heat. Ask the plumber to either repair the gas valve or if the damage is irreparable then replace the old valve with a new one.

Mineral Built-Up

To descale the mineral deposits the tank-less water heaters need to be flushed often. These mineral deposits can accumulate over time and destroy the heating element. Mineral deposits can cause the unit to shut off all of a sudden.

Also, these mineral deposits can destroy the heating element completely. Installing a water softening unit lessens the need for frequent flushing. If you have a hard water supply try flushing at least once a year to protect your expensive unit from getting damaged.

The tankless water heating unit can last for a very long time when taken proper care of. Industry professionals suggest a tankless water heater can function well for up to 20 years. When a water heater is not routinely flushed and mineral builds up inside the unit, it will cause the pipes to leak and thus cause a need for replacement.

Improper Installation

Installing a tankless water heater all by yourself might not be an easy job. If you want to do so then go through the manual to get some idea about where to place the different parts. It can happen that some issue at the time of installation might cause the unit to corrode later.

One such example is the use of dielectric unions to connect the pipes. The dielectric unions are used when connecting two different types of pipes. When used for the same pipes the dielectric unions cause the pipes to corrode. For tankless water heaters, brass fittings are used for making connections.

  • If the temperature of the water heater is set too low then it also can cause the unit to shut off.
  • Using a water-saving showerhead might be the cause of this problem.
  • Damage to the water flow sensor causes the unit to shut off.
  • Venting pipes should have an appropriate length and shouldn’t be too short.
  • Gas pressure needs to be maintained at a certain level so the heating system will function right.

Low Water Flow Level

Less water pressure makes it hard to do simple daily chores. If your tankless water heater water pressure is too low then use only one faucet at a time. Make sure multiple water-using applications at not being used simultaneously.

Check your water supply to make sure that the issue is not with your incoming water supply.

If the gas pressure is low the unit automatically reduces the water pressure to keep the temperature stable.

The plumber should make sure no problem with water connections. All the fixtures and pipes are functioning totally fine.

Why does the Tankless Water Heater Shut off During Shower?

If you own a very old tankless water heater then surely it will have a low minimum flow rate. Flow rate is the amount of water that must flow through the pipe for the heating unit to heat up the water.

If your water demand is below the unit’s lower flow unit then it shuts off as part of a safety precaution. If enough cold water is not supplied to the heat exchanger it might overheat and get damaged. To avoid this huge loss the unit shuts off. To solve this issue ask your technician if you can upgrade your unit.

The latest unit has a more suitable low flow rate. The lowest water flow rate ensures that the unit will run fine even if you need a very little amount of water.

Tankless water heaters are often preferred over the traditional units for being more energy-efficient and low maintenance. Like all other units, they are not immune to problems. In this article, we have listed some common problems with their solution.

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.

1 thought on “Common Tankless Water Heater Problems”

  1. Can I use electric water heater if I don’t have gas on to heat water it has been shut off I have water but it’s cold water

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