Noisy Water Heater? How to Stop the Knocking/Bubbling


A noisy water heater can be annoying and potentially indicate underlying issues with the unit. Here’s a brief summary of common causes of noisy water heaters and their solutions:

1. Sediment Buildup:

  • Cause: Over time, mineral sediment can accumulate at the bottom of the tank, leading to popping, crackling, or rumbling noises during heating.
  • Solution: Drain and flush the water heater to remove sediment buildup. This should be done annually as part of regular maintenance.

2. Thermal Expansion:

  • Cause: When water is heated, it expands, which can create pressure in the tank. This pressure can lead to loud banging or knocking sounds.
  • Solution: Install a thermal expansion tank or pressure-reducing valve to regulate the excess pressure and prevent noise.

3. Loose Heating Element or Dip Tube:

  • Cause: Loose heating elements or dip tubes can vibrate and make tapping or knocking sounds.
  • Solution: Tighten or replace any loose heating elements or dip tubes to eliminate vibrations.

4. Water Hammer:

  • Cause: Water hammer occurs when fast-closing valves or faucets create sudden pressure changes in the plumbing system, leading to loud banging sounds.
  • Solution: Install water hammer arrestors or adjust water pressure to prevent water hammer. You can also add air chambers to absorb shock.

5. Expansion and Contraction of Tank:

  • Cause: As the water heater heats and cools, the tank expands and contracts, causing creaking or popping noises.
  • Solution: Properly secure the water heater to minimize movement and reduce noise. Padding or insulation can help dampen sound.

6. T&P Valve Operation:

  • Cause: The Temperature and Pressure (T&P) relief valve may release excess pressure or temperature, resulting in a hissing or gurgling sound.
  • Solution: Ensure that the T&P valve is working correctly and is not leaking excessively. If needed, replace a faulty valve.

7. Tank Corrosion:

  • Cause: Corrosion inside the tank can create weak spots or cracks, leading to leaks and unusual noises.
  • Solution: If you suspect tank corrosion, it’s best to consult a professional plumber or replace the water heater if necessary.

8. Air in the Tank:

  • Cause: Air bubbles trapped in the tank can make gurgling or bubbling sounds as they rise.
  • Solution: Bleed the air from the water heater by opening the T&P valve slightly until water flows steadily. Be cautious, as the water can be hot.

Source of Water Heater Sediment

Sediment in the water heater comes from 2 places. The first and main one is the water itself and the other one is the water heater anode rod.

Water contains dissolved minerals like iron, calcium, manganese and others. While the minerals are not dangerous to the human body, the same cannot be said about water heaters.

Areas with hard water are especially affected by water heater noises than areas with soft water, since hard water has a high concentration of minerals. The minerals settle at the bottom of the water heater tank, reducing its volume with time.

Water heaters have an anode rod at the middle which is specifically designed for sacrificial purposes. In most water heaters, the anode rod is usually made of magnesium.

How this rod works is that minerals present in the water react with it instead of the water heater inner lining, thereby extending the life of the water heater.

As the elements in the water react with the anode rod, it wears out and breaks down settling at the bottom of the tank forming a sediment. Anode rods should ideally be replaced after 5 years.

As you already know, the heating elements of water heaters are located at the bottom of the tank. This means that sediment will collect on top of the heating element, trapping some water as a result.

As the water trapped by the sediment layers is heated, it starts boiling and bubbling and within no time the bubbles begin to escape from the sediment layers and hence the bubbling and popping sounds from the bottom of the water heater.

To understand this better, imagine you are heating a covered pot full of water on a stove. As the water gets hot, it starts to boil and bubble about, which has a distinct sound. At some point the bubbling water will even try to push the lid up and out of the pot.

When water is boiling, it moves rapidly inside the water heater. That can also cause layers of sediment to move around and when they come in contact with the water heater tank cause knocking/rattling sounds.

Is It Dangerous?

A noisy water heater is not exactly dangerous. There is no risk of it exploding if the temperature and pressure relief valve is still functional. The sediment however makes it inefficient (and therefore expensive to run) and could also cause a leak at the bottom necessitating a replacement.


The main reason a noisy water heater is inefficient is due to the fact that the sediment reduces the volume of the tank, hence only a small volume of water can be heated at a time. If your hot water runs out quick while at the same time your water heater makes noises, just know you have a substantial amount of sediment in the tank.

A noisy water heater also takes longer to heat the water since there is no free circulation of heat due to the sediment. You will therefore notice an increase in your gas or electric power bills.

To test whether your noisy water is at risk of exploding, lift off the lever on the T&P valve gently. If the valve discharges water, then the water heater is safe. On the other hand, if no water comes out of the valveā€™s discharge tube your water heater is at risk of exploding and you need to replace the valve as soon as possible.

How to Fix It

Fixing a noisy water is in most cases an easy fix that you can do on your own without calling in a plumber. If you must call in a plumber, make sure they are well experienced working with water heaters.

The first thing to do to fix a noisy water heater is to flush it. Flushing a water heater is basically draining the water in the tank, and then flush out sediment with more water.

How to Flush a Water Heater

  • Turn off the water heater. If you have an electric water heater turn off power at the circuit break while with a gas water heater you will need to turn off gas supply to the pilot. Draining a water heater with the heating element still on will burn it.
  • Turn off the cold water supply. There is a shut off valve on the cold water pipe to the water heater. Turn it clockwise if it is a gate valve but for a ball valve bring the lever to 90 degrees of the supply pipe.
  • Connect a garden hose to the water heater drain valve. Direct the end of the hose to a floor drain or out in the driveway. Warn everyone around of your intentions since the water will be scalding hot.
  • Turn on the nearest hot water faucet. This will help water drain out of the drain valve faster, while at the same time preventing having an airlock in the system.
  • Use a flathead screwdriver to turn on the drain valve. Water will start draining out of the tank through the hose.
  • Keep monitoring the quality of water as it drains out. As you will notice, the last bit of water to drain out will be quite dirty. Drain out all the water.
  • When no more water is draining out of the hose, turn on the cold water supply valve. The water will strike the bottom of the tank hard and agitate the sediment still there and forcing it out of the tank. Do this until only clean/clear water is flowing out of the hose

Note: If you suspect that the sediment in your water heater is too thick to be flushed out, you can dump 1 gallon of vinegar inside the tank after draining it. The vinegar will break down and dissolve the sediment making it easy to flow out.

You do that by removing the T&P valve and pouring the vinegar using a funnel. Wait for 1 hour then turn on the water to agitate the sediment further.

  • Once you are happy that most of the sediment has been flushed out, turn off the drain valve and disconnect the garden hose.
  • Turn on the water supply shut off valve. If you had turned off the cold water supply turn it on and start filling the tank.
  • To avoid having air trapped in the water heater and water pipes, keep the nearest hot water faucet open. This will flush out the air in the pipes. At first, water will be sputtering out of the faucet but once air has been completely flushed out you will have a soft stream of water. Only then should you turn off the faucet.
  • Turn on the water heater. Power up the water heater at the circuit breaker or turn on the gas supply to the pilot if you have a natural gas water heater.
  • Hang around the water heater for about 20 minutes, listening for any sounds as the water is being heated.

In most cases, flushing the water heater is usually enough to fix/stop a noisy water heater. If that does not work you will need to call in a professional plumber.

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