Why Is My Water Heater Making a Knocking Noise?

A knocking sound coming from your water heater is usually caused by sediment collecting at the bottom of the tank. The noise is often harmless at first, but it should not be ignored. As water heats up, trapped sediment hardens and causes popping or banging sounds as steam pushes through it. We often hear from homeowners dealing with this issue before they call for water heater repair in Chandler, AZ, especially when the noise starts getting louder during normal use.

What Causes the Knocking Sound?

Minerals like calcium and magnesium naturally exist in many water supplies. Over time, those minerals settle inside the tank and form a thick layer of sediment. When the burner heats the water, pockets of steam burst through that buildup and create the knocking noise.

Other possible causes include:

• High water pressure causing water hammer in nearby pipes (not the tank itself)
• Loose or unsecured pipes near the unit
• Failing heating elements (in electric water heaters, often causing humming or sizzling rather than knocking)
• Excessive sediment causing overheating at the tank bottom (more severe cases)

If the tank is older and making noise regularly, it may be time to consider water heater replacement before the buildup shortens the system’s lifespan.

A 3-Step Troubleshooting Checklist

Before scheduling service, there are a few things homeowners can check safely.

1. Listen to When the Noise Happens

Pay attention to when the knocking starts. If it only happens while the tank is heating, sediment buildup is the most likely cause. Rumbling or popping during heating cycles is common in gas and electric units.

2. Check the Water Temperature

Water that is set too high can increase pressure inside the tank and make noises more noticeable. The U.S. Department of Energy recommends setting most residential water heaters to 120 degrees Fahrenheit for safety and energy savings.

3. Look for Signs of Leaks or Rust

Small leaks, rust-colored water, or moisture around the tank may point to internal wear. Once corrosion develops inside the unit, repeated repairs often become less practical and reliable over time.

Why Flushing the Tank Helps

A professional tank flush removes sediment before it hardens into a dense layer. Regular flushing can improve heating performance, reduce strain on components, and help the unit run quieter. Homes with hard water often need this service more frequently because mineral buildup happens faster.

Ignoring the noise for too long can force the system to work harder and increase utility costs. Some homeowners also notice inconsistent hot water or longer recovery times once sediment becomes excessive.

Sounds Your Water Heater Should Never Make

Not every sound is tied to sediment buildup issues. Some noises point to more serious mechanical issues.

Call your water heater installation technician if you hear:

• Sharp screeching
• Metal grinding
• Loud hissing near valves
• Repeated banging from pipes inside walls

These sounds may involve pressure problems, failing components, or loose plumbing connections.

Frequently Asked Questions

Can sediment damage a water heater?

Yes. Thick buildup traps heat inside the tank and places added stress on the bottom surface and heating components.

How often should a water heater be flushed?

Most manufacturers recommend flushing once a year, though homes with hard water may need it more often.

Is a noisy water heater dangerous?

Usually no, but persistent knocking should still be inspected before the buildup affects performance or damages internal parts.

Restore Quiet, Reliable Hot Water

Strange noises rarely disappear on their own. Gold Star Plumbing & Drain provides fast diagnostics, same-day service options, and 24/7 availability for homeowners dealing with noisy water heaters. Our licensed and insured technicians bring over 25 years of industry experience, fair pricing, financing options, warranties, and support backed by more than 1,400 satisfied customers and an A+ rating from the Better Business Bureau.

If your water heater keeps knocking, call us today to schedule a service.