To book a service appointment please call 833-HVACMAN

Why Do My Water Heaters Make a Loud Knocking Noise?

Noise coming from any appliance can be a cause for panic and worry for homeowners. It’s common with some appliances while others sit quietly forever. However, sometimes the presence of any noise squeaking out of an appliance shouldn’t necessarily cause great concern. Your water heater making a knocking or popping sound might be just that.

The knocking or rumbling noise in the water heater tank is most likely because of a settlement of a thick layer of sediment at the bottom of the tank, also called “scale.” It’s a common occurrence in some areas. The solution isn’t difficult, either. The tank may need flushing.

Furnace Tune-Up In Westminster, Garden Grove, Fountain Valley, CA and Surrounding Areas

What is Scale?

The sediment or mineral deposits at the bottom of the tank are called scale. The minerals (like calcium and lime) may be present in your water and are the source.

Water inherently doesn’t contain any minerals. When it rains or snows, water is mostly in pure form.

However, minerals like calcium, magnesium, and potassium are present in rocks. They get picked by the water when it gets in contact with soil or rocks. Don’t worry; in most cases, the minerals are harmless. They might even benefit your health.

Depending on the local geography, the water might be hard or soft (mineral-less). Some minerals are essential to the human body but not so necessary for your water heater. The deposit of minerals builds over time and ends up damaging your water heater.

How is the Knocking Noise Caused?

Once the sediment buildup is significant, it starts causing problems. The heating element in the heater is at the bottom of the tank, where the sediment is deposited. The heating element hardens the sediment during regular usage.

The hardened sediment traps the water under it and, under high temperatures, creates pressure. The water trapped under the sediment tries to escape, rattling around and making knocking or popping sounds inside the tank. It’s similar to how the untightened lid of a boiling kettle makes noise when it comes under high-temperature pressure.

A quick solution is flushing the tank. Flushing removes this sediment, and water can no longer get trapped.

What If the Heater is Left Without Flushing?

It’s strongly recommended that you flush the water heater whenever necessary. You could either do it yourself with the steps explained below or get a technician for help. The sediments not only cause the knocking noise but make the water heating process difficult.

In simple words, your heater is struggling. It now runs longer than the usual time required to heat water, leading to overheating issues. Overheating is what you don’t want – it damages the tank’s protective inner lining and deteriorates the effectiveness of the heating element in the long run.

How to Flush the Water Heater Tank?

Here are the steps required to be followed to flush the tank properly. Luckily, the steps aren’t difficult and should be simple enough, even for beginners. Put on some heat-resistant gloves, preferably, before you get started.

  • Turn off the power supply of the water heater. If you have a gas water heater, set the gas supply to pilot or vacation mode.
  • To prevent further cold water from entering the water heater, close the cold water shutoff valve.
  • Turn on the nearby hot water faucet (kitchen or washroom). This will prevent any vacuum and ease the draining. Leave the water heater for about 20-30 minutes to cool down.
  • Connect a garden hose to the water heater’s drainage spigot at the bottom of the tank.
  • Make sure to put the other opening of the garden hose in a safe location for drainage, like a large bucket or basement drain
  • The water heater tank is ready to drain. Open the drainage valve and let the water flow out. The initial water might be dirty; that’s the sediment coming out – just some of it.
  • Time to flush the tank. Carefully flush out the sediment. Turn the cold water on and off alternatively to make sure no residue remains.
  • Once the cleansing is done, close the drain valve, remove the hose and let the cold water flow in the heater.
  • Turn the power supply back on. You’re all set now.

How Often Should You Flush the Water Heater?

Ideally, the water heater should be flushed once a year. If you notice any hint of knocking or popping sound before that, it would be wise to flush. It’s a straightforward process, as explained, and won’t take much of your time.

How An Air Conditioning Upgrade Can Drastically Lower Your Electric Bill?

Should You Treat the Hard Water?

If your tank is sedimented too often, the hard water might be too hard. It might damage other appliances, clog the plumbing, damage your clothes, and irritate skin and hair.

It would help if you considered treating the hard water by installing a water filtration system, which could be expensive, but a one-time fix. A cheaper alternative is to use a water softener for daily purposes.

If your water heater is making strange sounds, it may also mean you’re overdue for service. We here at Absolute Airflow can come out and inspect your water heater and let you know if it’s time to replace it. Please contact us today to learn more or schedule a service check with our team of professional technicians.

For Quick Emergency Help – Please Call (833) 482-2626 Immediately

Our state-licensed and certified HVAC technicians are always available to help you.

Absolute Airflow is a 24 Hour Emergency HVAC Service Contractor

Customer Reviews

Claudia M.

Scott, along with his associate, Gabe, did a great job. They were both professional and friendly. Scott explained in enough detail to help me understand how my a/c unit works-he’s very informative. Have was a great help, cutting the time it took to clean and install the HVAC equipment. I liked that they were both pet friendly, that’s also important for me. I’ve been a customer of absolute Airflow for a couple of years and they are a great company …

Ty S.

Have had nothing but amazing experiences with Absolute Airflow from the beginning. We have had a few issues here and there but Absolute has always sent someone out quickly and stood behind their work. Most recently they sent out Spencer and he was the best technician we’ve ever had! He was extremely respectful and polite, he also took the time to thoroughly talk me through and help me understand the genesis of our various issues we were encountering. Definitely hope …

Ian S.

My requested service was set up by Marcus who came to my home to evaluate and was prepared with options and great prices for my water heater replacement. Was able to get an appointment within 3 days as there was no emergency. My install tech James was amazing, He was very respectful and maintained a clean and organized work area as the installation was in the home. The removal, prep, and installation of new water, gas, and venting took approximately …

Richard S.

I can’t express enough how impressed I am with this company and especially Anthony Belt. Anthony was so thorough and patient with my wife and me. The impressive part was he was able not only to identify all the problems with my heating and ac but went above and beyond to fix all of them! My electrical bills were over $500 a month during the ac months and now they are less than $200! Not only am I saving a …

Patrick K.

I haven’t posted any reviews in a long while but here I am thanks to SCOTT with Absolute Airflow. The warmer Cali weather is around the corner and as a responsible homeowner, I decided to get my HVAC system checked out and tuned up before the summer heat. Scott provided us with the full red carpet experience. His knowledge, quality and care put into his work, and professionalism were all outstanding. Replaced fan motor due to oil leak (a normal …

Liem H.

Outstanding experience from the start. I’ve been a member of Absolute Airflow for almost 2 years now. Since then, I’ve had my system maintained twice a year. Every service has been very thorough and professional. Each time, everything was explained to me in terms that I would understand, coupled with plenty of photo documentation. Which I appreciate so much. Knowing that I would have to replace my aging system. I dreaded the coming expense and experience. But my fears were …