A tankless water heater is a helpful addition to your home, providing hot water whenever needed. However, it can be incredibly frustrating when it suddenly stops giving you hot water. In this blog post, we’ll look at five common reasons why your tankless water heater might not deliver hot water and provide simple solutions for each issue.

1. No Power To The Unit

Tankless water heaters need both electricity and gas to work. If there’s a problem with either of these power sources, your heater won’t be able to heat water.


  • Make sure you plug your heater into a grounded electrical outlet (the regular kind you use for most appliances).
  • Check itself is working correctly. If it’s not, get a certified electrician to fix it.
  • Rotate the gas control valve to the ‘On’ position.
  • Check that the gas supply pressure matches the type of gas you’re using, whether natural gas or propane.

2. Dirty Cold Inlet Water Filter

If the filter that catches dirt in the cold water supply is clogged, your tankless water heater won’t get enough water to heat.


  • Turn off the water heater and the gas valve.
  • Shut off the water supply to your plumbing system or close the water supply valve.
  • Open all your hot water faucets.
  • Now, it’s time to clean the clogged filter. Detailed steps are in the ‘How To Fix’ section.

3. Defective Flow Sensor

A flow sensor helps the heater control the flame to heat the water properly. If it’s not working right, you’ll get cold water instead.


  • You’ll need to replace the flow sensor. Call a technician to help if you’re uncomfortable doing this yourself.

4. Dirty Heat Exchanger

Over time, minerals and scale can build up in the heat exchanger, making it less efficient at heating water and causing a lack of hot water.


  • The answer here is descaling your water heater. You’ll need equipment, including a 5-gallon plastic bucket, a cleaning solution, hoses, and a water circulation pump. 

5. Defective 3-Way Valve

The 3-way valve helps control the water flow within the heater. If it’s not working correctly, you won’t get hot water.


  • Replacing the 3-way valve can be complicated, so hiring a professional for this task is best.


It can be frustrating when your tankless water heater stops providing hot water. But don’t worry, you can usually fix the problem. These five issues we’ve discussed are the most common reasons for no hot water, and the solutions provided can help you get your hot water back.

So, if you’re tired of chilly showers disrupting your daily routine, take action and get your tankless water heater working properly again. “Experience the Comfort of On-Demand Hot Water!”

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