Tankless Water Heater Shuts off During Shower: 6 Easy Fixes

The last thing you need in the middle of your relaxing, hot shower is cold water out of nowhere because your tankless water heater shut off.

If your hot water heater tends to shut off randomly during your shower, there is something wrong with some of its vital components, the water pressure or the gas supply if you have a gas water heater.

Please stick with us as we go through the most common problems causing the tankless water heater to shut off during the shower and the most effective solutions to this issue.

Why your tankless water heater shuts off during shower?

If your tankless unit suddenly shuts off, it is clear that there is an issue with the system and it could be a faulty component or a more complex problem.

Either way, troubleshooting your gas or electric water heater will help you get to the bottom of this issue.

1. Cold water sandwich

A cold water sandwich occurs when hot water is used, causing the tankless water heater to shut off

This can happen if there is a high demand for hot water (such as multiple people taking showers at once) or a restriction in the water flow (such as a clogged pipe). 

When dealing with this issue, you will notice that the hot water only runs for a short period before turning cold. 

2. Clogged tankless water heater

Another potential problem is that the water heater is clogged.

Mineral buildup or debris can block the flow of water, causing the heater to shut off. 

Clogs can affect every component of the heater, including the heat exchanger, burners and venting system.

To fix this issue, it may be necessary to flush out the water heater and possibly replace any damaged components. 

It is also important to regularly flush and maintain your tankless water heater to prevent clogs from occurring in the first place.

3. Gas burner or gas line issue

A gas burner or gas line issue might be causing the sudden shut-off.

Contacting a professional to inspect the gas line and burner for any potential safety hazards is essential. 

The problem with the gas burner might be that it is not receiving enough gas, causing it to shut off.

It could also be a clogged burner or faulty ignition

Another possibility is an issue with the gas line, such as a blockage or leak.

4. Faulty thermometer or pressure valve

A faulty thermometer or pressure valve could be the culprit for your tankless water heater shutting off during the shower. 

In this case, it is possible that the thermometer or pressure valve is not correctly sensing the temperature or pressure in the unit, causing it to shut off prematurely. 

The role of the thermometer in your tankless heater is to monitor the water temperature and shut off the heating element once the desired temperature is reached. 

On the other hand, the pressure valve regulates the incoming water pressure to prevent any damage to the unit. 

If you suspect either of these components may be faulty, it is best to seek professional assistance for proper diagnosis and repair

5. Not enough water

The tankless water heater could shut off during the shower because it isn’t drawing enough water

This happens when multiple showers or faucets are running simultaneously, causing a decrease in water pressure.

In this case, installing a larger water heater or upgrading your plumbing system to handle the demand may be necessary.

6. Faulty heating element

The role of the heating element in a tankless water heater is to heat the water as it passes through

If the heating element is faulty, it may not be able to heat the water effectively and may shut off during use.

The heating element could be clogged or need to be replaced if it is damaged or simply malfunctioning

How to fix a tankless water heater that shuts off during a shower

If your water heater shuts off abruptly, it is necessary to inspect all of its components closely and detect the core issue. 

This way, you’ll be able to prevent the water heater from malfunctioning in the future.

Here’s how you can fix a water heater that shuts off during shower.

1. Solve the cold sandwich issue

First, check if the water flow rate is within the recommended range for your tankless water heater.

If it is too low, try adjusting the water pressure

Next, check for any gas or electrical issues causing the shutdown.

If necessary, call a professional to diagnose and fix any problems. 

Lastly, make sure to properly maintain and clean your tankless water heater to prevent future shutdowns. 

This may involve flushing out sediment buildup or replacing faulty parts.

Overall, with some troubleshooting and proper maintenance, you can solve the issue of your tankless water heater shutting off during showers.

2. Descale the water heater

To descale the water heater, turn off the power, drain any remaining water and clean out all sediment buildup using a descaling solution or vinegar.

Check for clogs in the water lines or low water pressure if the issue persists. 

Another method of cleaning a tankless water heater is to flush it using a garden hose, removing any buildup in the pipes. 

If the issue remains, it may be time to call a professional or consider replacing the water heater altogether

It is essential to regularly maintain and clean your water heater to ensure optimal performance and hot water for showers.

3. Check the gas burner and gas line

To troubleshoot the gas burner, check the gas supply valve to ensure it is fully open.

Next, clean the burner assembly and ignition components. 

If the problem persists, it may be an issue with the thermostat or gas pressure.

It is recommended to contact a professional for further assistance. 

In the meantime, you can use hot water from another source, such as a traditional tank water heater.

A clog in the gas line can be solved by cleaning or replacing the gas filter.

Be sure to shut off the gas supply before attempting this fix. 

On the other hand, if the gas line is leaking, it is essential to contact a professional immediately, as gas leaks can be dangerous.

Check the circuit breaker or fuse if the water heater uses electricity to ensure it has not tripped or blown. 

Resetting or replacing it may solve the issue.

It may also be helpful to clean any mineral buildup on the heating elements. 

In some cases, the problem may lie in faulty wiring or a defective heating element, which will require professional assistance. 

As a precaution, regularly inspect and maintain your tankless water heater to prevent future shutdowns during showers. 

This includes checking for gas leaks, cleaning components and ensuring proper ventilation.

Remember that sudden fluctuations in water pressure can also cause the unit to shut off temporarily. 

Adjusting the water pressure regulator or installing a water pressure booster pump may help alleviate this issue.

4. Check the thermometer and pressure valve

If you’re dealing with a faulty thermometer or pressure valve, it could be causing your tankless water heater to shut off during showers. 

To fix this issue, you may need to replace these components or have a professional inspect and repair them. 

Here are the steps to replace a thermostat in your tankless heater:

  1. Turn off the power or gas supply to the unit.
  2. Remove the cover and locate the thermostat.
  3. Disconnect wires and remove the old thermostat.
  4. Install a new thermostat and reconnect the wires.
  5. Place the cover back on and turn on the power or gas supply. 

To replace a faulty pressure valve, you will need to:

  1. Turn off the water supply to the unit.
  2. Remove the cover and locate the pressure valve.
  3. Disconnect any pipes or wires connected to the valve.
  4. Replace with a new pressure valve and reconnect any pipes or wires.
  5. Turn on the water supply and place the cover back.

If you are unsure about replacing these components yourself, it is best to call a professional for assistance to ensure proper repair and safe operation of your tankless water heater.

5. Check if there is enough water

If the water heater cannot draw enough water, you may need to lower the temperature setting or install a larger unit

It could also be an issue with the water pressure or a clogged filter that needs to be cleaned or replaced.

6. Fix the heating element

Finally, if the problem is a malfunctioning heating element, it may need to be cleaned or replaced.  

To locate the heating element, you will need to shut off the power and water to the unit, remove the access panel and then disconnect and replace the faulty heating element.  

However, if you don’t have much experience in this area, it is advised to consult with a professional for this type of repair. 

Related: A.O. Smith vs. Rheem Water Heaters

Related: Why Does My Tankless Water Heater Sound Like a Jet Engine

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