9 Common Reasons Why No Hot Water

If you’re not getting the amount of hot water you’d like from your tankless water heater, there are many reasons why you might be experiencing a lack of hot water. While every household’s needs are different and will have unique factors affecting performance, there are a few general things that can cause your water heater to underperform. Some issues may be caused by your tankless water heater itself, others may be the result of problems with your home’s plumbing or heating system.

If you are experiencing problems such as no hot water but heating works perfectly fine with your tankless water heater, tankless water heater goes cold after a few minutes or no hot water to kitchen sink it is important to diagnose the issue as quickly as possible. Faulty equipment can lead to decreased efficiency and increased utility costs, and may even pose a danger to you and your family

why is my tankless water heater not heating

Here are nine of the most common reasons your tankless water heater might not be providing you with enough hot water:

1. Improper installation

This is one of the most common reasons for tankless water heaters not performing as expected. If your unit is not properly installed, it can lead to a wide variety of problems, including inadequate heating, less water flow and no hot water when the taps are turned on. Correct installation of tankless heater is pretty crucial to enjoy hot water when needed.

2. Incorrect sizing 

Another common issue is an improperly sized unit. There are many sizes available for water heaters. Choosing the right size is dependent on your household needs. There are some serious problems associated with having a small or large sized tankless water heater for your household. In a household with a small water heater, there is simply not enough hot water for everyone. It is possible to overload your tankless water heater if many faucets are turned for hot water simultaneously. Therefore, make sure you choose the correct sized tankless to meet your hot water demand smartly.  

3. Sediment Buildup

Tankless water heaters are especially susceptible to sediment buildup, which means they should be regularly checked for buildup. Additionally, Sediment and mineral buildup also clog the water pipelines and diminish the flow of the tankless water heater. Therefore, to maintain their optimal performance, they should also be descaled every year. 

4. Failed Ignition

Another possibility is that your house’s lack of hot water is caused by an ignition failure. The presence of an error message on your water heater can be an indication that you might have an ignition issue. Usually, this is the result of an issue with the supply, such as an empty propane tank or closed gas valves. On the other hand, failing to ignite can be a sign of a more serious or complicated problem, such as an electrical issue. The best thing to do if you see an error message is to contact a professional plumber.

5. Blocked Exhaust or Air Supply

It is possible for your tankless water heater to stop heating when your exhaust or air supply is blocked. Another reason could be that the vent pipe might have become disconnected or has a hole in it. 

As part of their safety measures, water heaters usually automatically power off to secure the appliance and to stop other situations that could result in injury. It is recommended that a water heater should be installed at a place where there are no other appliances or where birds cannot build nests, another significant cause of blockage or damage to the venting.

6. The Temperature Is Set Too Low

One of the most common reasons for cold water from a tankless water heater is that the temperature is set too low. To fix this, increase the temperature setting on your water heater.

7. No Power or Gas

That’s right — no power or gas could be the big reasons for no hot water! Check the main electrical panel if your home is powered by electricity. There may have been a problem with the breaker, demanding a reset before your tankless water heater can be used again. Similarly, if you are using tankless heaters powered by gas, ensure the gas valve is fully turned on, your bill is paid, or you have proper propane supply.

8. Thermostat

Sometimes the reason for not delivering hot water is that the thermostat is not set properly on a tankless heater. It is usually recommended that the thermostat must be reset at around 120 F for sufficient hot water. 


The tankless water heaters use more amps to run properly. They normally require 120 amps to work smartly. It is a common mistake for homeowners to incorrectly connect a battery-powered water heater to a standard 110-volt electrical outlet. To be safe, you should have a battery water heater plugged into a dedicated, battery-circuit breaker. Also, the water heater should be unplugged when not in use. If your home was built in the past, it is also recommendable to update the electric panel. 

How to Reset Tankless Water Heater

If your tankless water heater has failed to heat any water, then you may need to reset it. Resetting the water heater will eliminate any problems that have caused the unit to not heat water. Resetting a tankless water heater usually involves the following:

  • First, turn off the power and gas supply to the water heater.
  • Next, allow the water heater to cool for several minutes.
  • After that, check the thermostat to ensure that it is set to heating mode.
  • If the thermostat is set to heating mode, then try turning it to the off position.

If your water heater is still not heating, then you may need to reset it.

  • To reset your tankless water heater, you will need to follow the tankless water heater instructions.
  • Finally, turn the power supply back on and check for water.

Daniel Adley is a seasoned and skilled plumber with over 20 years of experience. Specializing in repairing and optimizing water appliances for large buildings, offices, and homes, he has a keen eye for efficiently identifying plumbing and maintenance issues. With a passion for his craft, Daniel brings extensive knowledge and expertise to every project, ensuring reliable and effective solutions for his clients.

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