Water Heater Knocking Sound? 3 Ways to Fix It5 min read

In most homes, the water heater is a pretty critical component. So, if you’ve suddenly noticed a water heater knocking sound, what should you do? Is it something to worry about?

To be honest, yes, it’s something to be concerned about (but not to panic over). A water heater is like any other appliance; it needs a little maintenance to keep it running smoothly and to reduce the need for repairs later on. 

A knocking sound from any appliance – whether that’s your washing machine, dryer, boiler, or water heater – is a sign that it needs some attention.

I’ve fixed this problem a few times before, so don’t worry: I’ll walk you through the causes, as well as how to fix it if you want to give it a try yourself.

I take information accuracy seriously therefore everything you’re about to read has been expert reviewed by Mark Longhurst, a professional plumber with over 15 years experience.

What Causes a Knocking Sound in a Water Heater? 3 reasons

Knocking sounds are weird, right? But this is actually a pretty common problem, especially in older water heaters. Here are a few common causes:

1. Sediment Buildup

Allow me to get technical for a second. Sediment buildup is what happens when minerals in the water supply itself settle at the bottom of the tank. This creates a kind of layer of sludge that insulates the heating element from the water, which means everything has to work harder than it should to heat up properly.

When the heating element becomes covered in sediment, it can make a knocking sound as it heats up the water – this is because little pockets of water get strapped beneath it, which turn to steam and make small explosions when they try to escape.

I know that sounds a little worrying! Signs that it might be sediment buildup include:

Before I can hear a knocking sound, I usually notice a leak from the bottom of the heater. The sediment clumps up and can cause leaks. Knocking only occurs when the sediment starts to disintegrate into pebble-sized chunks, which make that strange rumbling sound.

Mark Longhurst

2. Loose Heating Element

The heating element is the part of the water tank that heats the water, and it’s (obviously) a very crucial part. It’s usually made from a metal rod, surrounded by an insulating material, and it has an electrical connection that provides the power to heat up in the first place.

So if something happens to the heating element – like it gets loose, for example – it can cause strange knocking and rattling sounds inside the tank. As it heats up, it may move around slightly, banging against the edges.

You might notice that your water heater is taking longer than usual to heat up, or you may even notice leaks.

3. High Water Pressure

The ideal water pressure range is somewhere between 40 and 60 pounds per square inch. This is the safe zone, giving you enough water flow for most households providing water for showers, faucets, and other appliances.

But if the pressure dials up a little too high, you might start hearing a knocking or banging sound. This sound is known – and I know this sounds weird, but bear with me – a ‘water hammer.’ This occurs when the flow of water in the pipes suddenly stops, causing a shock wave to travel through the whole system.

When the pressure is too high, there may be a surge of water rushing through the pipes when a faucet or valve is closed. And this water creates a big wave of pressure which hits the sides of the pipes, causing a loud sound.

High pressure is a fairly urgent issue as it can cause some damage to your water heater such as overheating.

Simple at Home Fixes to Water Heater Knocking Sounds 

There are a few simple fixes I would recommend trying if you hear the knocking sound in your water heater.

Flushing the Tank

Flushing the tank is a kind of boring but useful job. I always say prevention is better than cure, and flushing the tank every now and then is a really good thing to do.

The steps are:

  • If you have an electric water heater, turn off the power supply at the circuit breaker. If it’s a gas water heater, turn off the gas supply valve and turn off the cold water supply.
  • Find the pressure relief valve. (It’s usually on the side of the tank near the top.)
  • Put on your protective gloves (on Amazon) as the water may be very hot.
  • Open it to relieve pressure. Attach a garden hose (on Amazon) to the drain valve at the bottom of the tank and make sure the other end of the hose is in a drain or outside (believe me, this is a hugely important step!)
  • Once the water is drained, turn on the cold water supply valve and let it run for a few minutes to drain out any sediment or debris.
  • Refill the tank by closing the drain valve and turning on the cold water supply valve. Once it’s full, you can switch on the power supply again.

Here’s a really informative video I found on how to flush your water heater tank (gas or electric):

Tightening the Heating Element

If you think it might be the heating element causing problems, you may be able to fix it yourself if you want to give it a try. Remember, safety is the number one priority and if you don’t feel comfortable or confident, leave this to a professional.

Here are the steps I would follow:

  • Turn off the power supply
  • Drain the tank
  • Locate the access cover (usually on the side of the water heater) and open it
  • Find the heating element and use a heating element wrench (on Amazon) to tighten it. Turn the wrench clockwise to tighten it.
  • Replace the access cover
  • Refill the tank
  • Switch it all back on

If you look at the heating element and it looks damaged in any way, call a professional: this is very much a job for them to deal with.

Here’s a cool video on how to replace the heating element. It could be useful to follow along even if you’re just looking to tighten your heating element:

Adjusting the Water Pressure

If it’s water pressure that is the problem, it’s a little harder to deal with. You can adjust it at the main valve, which should be found where the water main enters your home.

You’ll need to:

  • Turn off the water supply
  • Locate the pressure regulator valve (this may be attached to the main water supply or should at least be nearby somewhere)
  • Use a wrench to adjust the pressure regulator valve – turn it clockwise to increase pressure or counterclockwise to decrease pressure
  • Once you’ve adjusted it, turn on a shower or faucet to check the pressure
  • Repeat the process until the pressure is just right

If you’re having an issue with excessive pressure, it’s better to ask for a certified plumber to come and install a pressure relief valve in the tank. This will regulate water pressure inside the tank, giving you the best pressure for your household use.

Mark Longhurst

Here’s another video on how to adjust your house water pressure:

When to Call a Professional

If you’ve tried all this and nothing has worked, or you’ve inspected your water heater and the issue is worse than you thought it was, you will need to call a professional.

I know it can be a bit daunting to hire a new contractor to work in your home. Go for a personal recommendation (like from a friend or family member), or go for someone who has good reviews on Google.

How to Prevent Water Heater Issues

Unfortunately, sometimes appliances just kind of … give up. As they get older, they may just break down. And there’s not a lot you can do about those moments, so there’s no point in beating yourself up about it.

I do recommend the following steps to reduce the risk of your water heater breaking down:

  • Conducting regular maintenance, which is important to detect problems. It’s recommended to have a professional check out your water heater at least once a year
  • Get your water tested regularly to ensure the quality is high, as well as ensure you don’t flush anything down the drain that you shouldn’t (I really can’t emphasize this last point enough)
  • Make sure your water heater is installed by a professional, and do your due diligence when hiring one

Water Heater Knocking Sound – Key Takeaways

A water heater knocking sound is definitely something to fix, but it can be sorted at home if the damage isn’t too bad. You can fix it by:

  • Flushing the tank to remove excess sediment or minerals
  • Tightening the heating element to stop it from banging around inside the tank
  • Adjusting the water pressure to prevent further damage

If you do notice that the problem isn’t fixed or you’d rather leave it to a professional, absolutely call a plumber – they’ll be happy to advise you and fix the problem themselves.

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Hi, I'm Ed, and I run BuildFanatic! I enjoy providing the best possible information on a range of home improvement topics.

Mark Longhurst
Plumber at http://www.pipesmart.com.au/ | Website | + posts

Mark Longhurst is a professional plumber with over 15 years of experience, owns Pipesmart, and is our resident expert in all things plumbing.

Mark helps review plumbing-related articles for BuildFanatic to ensure we're providing our readers with the most accurate and updated advice.

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