Why is My Water Heater Making a Knocking/Rumbling Noise?

January 11, 2014

It’s scary. Hearing your water heater making such a loud knocking/banging noise. Especially in the winter time where the thought of being without hot water sends shivers down your spine.

Worry not! The problem is most likely that your water heater has sediment built up at the bottom of its tank.

We’ll explain why this is causing a loud noise and what you should do about it.

What sediment is and why it’s causing loud noises

The sediment in your water heater’s tank is made up of fine loose minerals (mostly calcium) from hard water. It looks like nasty sand.

What happens is, over time, tons of sediment sink to the bottom of your tank where the heating element is. Water gets mixed in and trapped underneath the sediment.

As your water heater’s burner heats that water, it creates steam bubbles that are violently escaping the sediment layers.

So that’s what’s causing the loud knocking/rumbling noise.

Here’s where things get scary

Really, the noise isn’t what you should be worried about (as scary as it sounds).

Since that sediment acts like a layer of insulation, your water heater’s burner is running longer. This:

  • Uses more gas/energy to heat the water to the desired temperature, increasing your utility bills.
  • Overheats the water heater’s metal tank, which over time, will deteriorate it, eventually leading to a leak and maybe even a flood.

Needless to say, you don’t want to deal that kind of disaster. According to disastersafety.org, “Water heater failures cost an average of $4,444 per incident after the deductible was paid.”

So think of sediment like plaque on your teeth. If the plaque is left alone, it will deteriorate your teeth. Similarly, the sediment causes your tank to deteriorate.

So what should you do to get rid of the sediment? Well, just like you need to get your teeth cleaned by a dentist at least twice a year, your water heater needs to be drained and flushed every 6-12 months.

DIY or get a professional?

Now, you can drain and flush your own water heater. You can find several instructions and tutorial on how to flush a water heater.

The main pro of DIY is obvious: you’re saving money. However, it’s going to take you time. And if you mess up, you can cause damage to your water heater's tank. So be careful!

We’re biased, of course, and suggest you contact a professional to drain and flush the water heater tank. We’ll even perform a general water heater maintenance check to make sure there’s no other problems.

Have another heating or air conditioning question for us? Contact one of our experts today.