Why Does My Water Heater Make a Knocking Noise?

Do you hear a knocking sound coming from your basement? Don’t be alarmed. You’re not the protagonist in some cheesy summer horror flick. What sounds like a poltergeist is most likely your water heater telling you it needs to be flushed. Your hot water heater should be flushed at least once a year to prevent sediment buildup inside the tank. If you can’t remember the last time you scheduled water heater maintenance, call one of our HVAC contractors today.

The last thing you want is for your hot water heater to stop working while you’re taking a shower. Scheduling water heater service will also help you save money in the long run by avoiding expensive HVAC repairs. If it’s been awhile since the last time the unit was flushed, we recommend hiring a HVAC technician to avoid having your water heater leaking.

Why does my water heater make strange noises?

Hard water contains minerals that are safe for humans, but wreak havoc on your hot water heater. Over time, these minerals settle on the bottom of your hot water tank. When you use your water heater, the high temperatures harden minerals into what we call “scale” and trap pockets of water. Eventually this trapped water turns into steam and breaks through layers of scale to create a popping or knocking sound.

How do I flush my water heater?

If you don’t feel comfortable flushing your water heater on your own, call one of our HVAC contractors to schedule water heater maintenance. The technician that comes out to your home will be able to flush your hot water heater so you don’t have to worry about sediment buildups for another year.

While you can flush a water heater on your own, we recommend hiring a professional if it’s been a few years. If you’ve scheduled water heater service regularly and think you want to DIY this year, follow our instructions below.

You will need:

  • Thick protective gloves
  • Garden hose
  • Flathead screwdriver
  • 5-gallon bucket (optional)

1.) Turn off fuel or electrical power.

Whenever you do repairs to your hot water heater, you will always need to shut off its power source. Depending on whether you have a gas or electric water heater, you will need to shut off the fuel or electrical power. Be sure to follow the manufacturer’s instructions.

2.) Turn off cold water supply.

Near the top of your hot water heater should be two valves. One is responsible for feeding in cool water and the other for sending out heated water. The valve you want should be clearly marked blue for cold water supply. Turn the valve 90 degrees to shut it off.

For your safety, we recommend that you wait overnight (or at least 30 minutes) for the water in your tank to cool down. If not drained properly, the scalding hot water could cause injury.

3.) Turn on hot water from nearby faucet.

While draining and flushing the tank, be sure to keep hot water running from a nearby faucet. Not only will this introduce air flow into your hot water heater to ease draining, but it will also prevent a vacuum from forming in your lines.

4.) Attach garden hose to drain valve.

When doing this step, be sure that you are wearing your protective gloves. Also make sure that the other end of the garden hose is placed in a safe area for the water to drain, such as a basement drain or bucket.

5.) Drain hot water tank.

When you open the drain valve, dirty water will come out through the hose. Don’t be alarmed. This merely shows that the sediment is being cleared from your hot water tank. Keep going until all the water is drained from the tank.

The water coming out may be extremely hot, which is why it’s important to wear your protective gloves. If you are using a bucket to drain the water into, you may need to empty your bucket several times during this process.

6.) Flush hot water tank.

When there is no more water coming out, you will need to make sure that there is no residual sediment left in the tank. Open and close the cold water supply valve a few times to disturb any residual sediment left on the bottom of the tank. Stop once the water comes out completely clear.

7.) Close tank drain valve.

Once you are done flushing your hot water heater, disconnect the hose, and close the tank drain valve. Also, make sure you shut off the hot water faucet you turned on earlier.

8.) Fill hot water tank.

Open the cold water supply valve to fill the water heater tank back up. To make sure there are no air bubbles in your lines, we recommend running all the hot water faucets in your home until normal water pressure returns.

9.) Turn power back on.

Once the tank is completely filled, relight your water heater by following the manufacturer’s instructions. Congratulations, your water heater is set for another year!

Our Grand Ledge HVAC contractors work hard to make sure your water heater runs efficiently. In addition to water heaters, we also offer services for your furnace and geothermal heating and cooling system. To schedule water heater maintenance, call Superior Home Comfort at (517) 925-1343.