How to Unfreeze a Tankless Water Heater: A Step-by-Step Guide


How to Unfreeze a Tankless Water Heater: A Step-by-Step Guide


In this article, we will discuss a common winter woe – a frozen tankless water heater. When the temperatures drop, it’s not uncommon for water heaters to freeze, causing inconvenience and potential damage. We’ll guide you through the process of unfreezing your tankless water heater safely and effectively.

Understanding Tankless Water Heaters

What Is a Tankless Water Heater?

A tankless water heater, also known as an on-demand water heater, is a system that heats water as it flows through without the need for a storage tank. It’s energy-efficient and provides a continuous supply of hot water.

Why Do Tankless Water Heaters Freeze?

Tankless water heaters can freeze when exposed to extremely cold temperatures for extended periods. Water inside the unit can freeze, leading to blockages and potential damage.

Signs of a Frozen Tankless Water Heater

Identifying the Problem

Before attempting to unfreeze your tankless water heater, it’s crucial to confirm if it’s frozen. Look for the following signs:

  1. No hot water supply.
  2. Strange noises from the unit.
  3. Reduced water flow.

Step-by-Step Guide to Unfreezing Your Tankless Water Heater

Turn Off the Power

The first step in unfreezing your tankless water heater is to turn off the power source. This is a crucial safety measure to avoid any electrical mishaps while you work on the unit. Follow these steps to safely turn off the power:

  1. Locate the circuit breaker or electrical panel in your home.
  2. Identify the circuit that supplies power to the tankless water heater. It should be labeled, but if not, look for a dedicated circuit breaker with a higher amperage rating, typically 30-50 amps.
  3. Switch the circuit breaker to the “Off” position. This will cut off the electricity supply to the water heater.
  4. Alternatively, if your tankless water heater is plugged into an electrical outlet, simply unplug it from the outlet to disconnect the power.

Disconnect Water Supply

The next step in unfreezing your tankless water heater is to disconnect the water supply. This is an essential precautionary measure to prevent further water from entering the unit while you work on thawing it. Here’s how to safely disconnect the water supply:

  1. Locate the water shut-off valve that controls the flow of water to your tankless water heater. This valve is typically located on the cold water inlet pipe leading to the unit.
  2. Turn the valve clockwise (right) to the “Off” position. This will stop the flow of water into the heater.
  3. After closing the valve, open a nearby hot water faucet to release any pressure and residual water in the system. This step helps prevent water from being pushed into the frozen areas of the tankless water heater during the thawing process.

Thaw the Unit

After turning off the power and disconnecting the water supply, the next crucial step is to thaw the frozen tankless water heater. Here are two effective methods to accomplish this:

1. Hair Dryer Method

  • Grab a hairdryer with adjustable heat settings and an extension cord if needed.
  • Set the hairdryer to low or medium heat to avoid overheating or damaging the unit.
  • Aim the airflow directly at the frozen areas of the tankless water heater.
  • Keep the hairdryer a safe distance from the unit and use it in a sweeping motion.
  • Continue this process until the ice inside the heater has completely melted.
  • Remember not to get the hairdryer wet during this process, as it can pose an electrical hazard.

2. Warm Towel Method

  • Soak several towels in warm water and wring them out so that they are damp but not dripping.
  • Carefully wrap the warm, damp towels around the frozen sections of the tankless water heater.
  • Replace the towels as they cool down to maintain a consistent thawing process.
  • This method may take longer than the hair dryer method, but it is a safer alternative.

Check for Damage

Check for Damage

After thawing the unit, inspect it for any damage caused by freezing. Look for cracks, leaks, or other issues that may need professional repair.

Reconnect and Test

Once you are confident that the unit is unfrozen and undamaged, reconnect the water supply and turn the power back on. Test the hot water supply to ensure it’s working correctly.

Prevention Tips

Avoiding Future Freezing

To prevent your tankless water heater from freezing again, consider these tips:

  1. Insulate the unit and pipes.
  2. Keep the area around the heater warm.
  3. Install a freeze protection kit if you live in an extremely cold climate.


Dealing with a frozen tankless water heater can be a hassle, but with the right knowledge, you can safely unfreeze it and restore hot water to your home. Remember to take precautions and, if needed, seek professional assistance.

FAQs (Frequently Asked Questions)

Can I use a space heater to unfreeze my tankless water heater?

While it’s possible, it’s not recommended as space heaters may pose a fire hazard. Stick to safer thawing methods.

How long does it take to thaw a frozen tankless water heater?

The time it takes depends on the severity of freezing and the thawing method used. It can range from a few hours to overnight.

Should I call a professional if I’m unsure about unfreezing my water heater?

If you’re not confident in your abilities or if there is any damage, it’s best to call a professional plumber.

Is it safe to use antifreeze in a tankless water heater?

No, using antifreeze in a tankless water heater is not recommended as it can damage the unit and contaminate your water supply.

Can I prevent freezing by running hot water continuously?

Running hot water continuously can help prevent freezing, but it’s not the most energy-efficient solution. Consider other preventative measures for better results.

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