How to Fix a Frozen Tankless Water Heater

While it’s hard to imagine, a tankless water heater can freeze even if it’s installed inside your home. Here’s what you can do to fix the problem. You’ll need to repair this situation quickly as freezing can cause damage and affect your running water and drainage. Do not attempt to operate the unit. If you find your tankless water heater frozen, here’s what you can do to thaw it out:

  1. Close the gas/water shutoff valves serving the water heater.
  2. Turn off the circuit breaker serving the heater.
  3. Give the system a chance to thaw, open the water supply valve, and see if water is flowing.
  4. Check the unit, its internal parts, your plumbing, and external pipes for signs of leaks
  5. If water is flowing normally, open the valves and turn the electricity back on.

It’s very important to contact a plumber if you notice any part of the water heater, or the pipes serving it, are leaking. Do not attempt to fix the unit yourself.

Preventing a Tankless Water Heater from Freezing

There are two ways to prevent freezing—by draining the water heater or setting the water to low flow.

1. Draining a Tankless Water Heater

If your tankless water heater is frozen and doesn’t have built-in freeze protection, you can drain it if a cold spell is coming and/or you’re going on vacation. Turn off the cold water and gas supply, temperature control, and electrical power. Open a hot water tap to relieve pressure. Then place a bucket under the unit to catch water; it is now safe to remove the drain caps on the hot/cold isolation valves. Hot water will then be released, under pressure, into the bucket. Next, remove the cold-water inlet filter and then the drain plugs on the bottom of the heater.

2. Running a Low Water Flow

Sometimes during the winter, the temperature may drop so low your tankless water heater can’t protect itself against freezing. Reducing water flow helps when there’s a power outage too. But you can prevent the unit and external piping from freezing up by turning off the power, closing the gas supply valve, and opening a hot water faucet. Now, you should only see about 1/10th of a gallon per minute flow (the water stream will not be more than .20 inches wide). The reduced flow of water leaves little left in your plumbing to freeze.

Winterizing a Tankless Water Heater

If you plan to be away all winter, you can winterize your water heater by turning off the gas, water, and power to the unit. First, turn off the cold-water supply, drain the unit by opening the solenoid valves (on both the cold and hot water lines), and turn on some hot water faucets. Then remove the inlet filter on the cold-water line to leave room for expansion should freezing occur.

If you can access the venting system, place a cover on the intake and exhaust vent to prevent debris or animals from getting inside and disrupting airflow. Another important method of protection is to insulate your pipes. Some insulators come with a pipe heating cable and thermostat to provide heating when it’s most needed.

Built-In Freeze Protection

Some models have ceramic heaters to protect against freezing; they can trigger automatically when the temperature drops to a certain level. Sensors can detect when the unit is below freezing if the primary heaters fail, turning the unit on and off to avoid freezing. Freeze protection solenoid valves (aka drain down solenoid valves) open automatically to drain the heater when power is lost. They’re more common with higher end models, but you can add them as well.

Contact Black Hills Inc. Home Services

If your tankless water heater is frozen, or otherwise not working as it should, we can fix it using the latest tools and techniques. Our technicians can take on any job, big or small. They’re licensed and bonded as well as thoroughly trained to successfully resolve any issue. Call 888-979-7946 today to request service.