What to Do if Your Hot Water Heater is Knocking

As an expert in home renovation with over 15 years of experience, I know that hearing your hot water heater knocking can be worrisome. But don‘t panic! In most cases, this is an easy fix. This comprehensive guide will provide you with everything you need to stop that knocking sound and get your hot water heater running properly again.

Why Does My Water Heater Knock?

Before we dive into repairs, let‘s first understand what causes the knocking noise in the first place.

Sediment Buildup

The most common culprit is sediment accumulation in the tank. Over time, tiny dirt and mineral particles from your water supply settle at the bottom of the tank. As the sediment builds up, it eventually hardens and expands when heated. This causes it to rattle around the tank, making knocking noises.

According to a study by the Water Quality Association, up to 75% of residential hot water heaters suffer from sediment accumulation that can lead to knocking.

Loose Parts

Internal components like pipes, relief valves, and baffles can shake loose over time, especially if subjected to high water pressure. When hit with hot, moving water these parts rattle around and knock against the interior tank walls.

High Water Pressure

Excessive water pressure entering the tank, usually over 80 PSI, can cause vibrations, water hammer noises, and knocking sounds.

Mineral Deposit Buildup

If you have hard water, mineral deposits like lime and calcium can accumulate along with sediment. As these mineral deposits expand and break free, they also create knocking noises.

How to Diagnose the Specific Cause

It‘s important to accurately diagnose the cause of the knocking sound in order to fix the problem. Here are some tips:

• Carefully listen to pinpoint the location and timing of the knocking noise. This can help you isolate whether it‘s coming from sediment buildup or loose internal parts.

• Visually inspect the exterior of the tank and pipes for any loose fittings or components that could be rattling against the tank.

• Check your home‘s water pressure. Pressure above 80 PSI can lead to knocking and rattling from water hammer effects.

• Drain a bucket of water from the tank‘s drain valve. Heavy sediment or mineral deposits in the water points to buildup.

• Consider the age and maintenance history of your heater. Older tanks (over 5-8 years) are more prone to sediment accumulation.

• Review your water quality report for total dissolved solids and hardness levels, which indicate sediment levels.

Step-by-Step: Draining and Flushing the Tank

If you‘ve diagnosed the issue as sediment buildup, flushing the water heater is often the quickest solution to stop the knocking noise. Here is a step-by-step guide:

Turn off Power and Water

Turn off power to an electric water heater at the breaker or unplug it. For gas water heaters, turn the gas control valve to "pilot" or "off."

Shut off the cold water inlet valve leading to the tank.

Open a hot water faucet inside the home to depressurize the tank and allow air in.

Connect Hose and Drain

At the bottom of the tank, connect a garden hose to the drain valve.

Place the other end of the hose in a bucket or direct it outside.

Open the drain valve and allow the water to empty into a drain area or bucket.

Flush the tank completely until the water runs clear with no sediment.

Refill the Tank

Close the drain valve and disconnect the hose.

Turn the cold water inlet valve back on to refill the tank.

Turn power or gas supply back on once tank is full.

Before Flushing

I recommend using a wire coat hanger to poke into the drain valve and loosen sediment beforehand. This allows more buildup to flush out.

Step-by-Step: Tightening Loose Parts

If the knocking is coming from internal components shaking and rattling, you‘ll need to open up the tank and secure everything:

Turn off Power and Water

Turn off power to an electric water heater or gas valve for gas heater.

Shut off the water supply and open a hot water faucet to depressurize the tank.

Open Tank and Inspect

Remove outer jacket panel and insulation.

Locate the source of the rattling noise.

Inspect fitting, pipes, valves, and internal baffles.

Tighten and Replace Parts

Use wrenches and pipe sealant/tape to tighten any loose fittings and pipes.

If necessary, replace worn out pipes, valves, or fittings. Consult replacement manuals.

Reassemble tank insulation and jacket. Make sure everything is secure.

Turn Water and Power Back On

Restore water supply and power/gas to the tank.

Adjusting Water Pressure

If your home‘s water pressure exceeds 80 PSI, the sheer force of water entering the tank can cause vibrations and knocking. Installing a pressure reducing valve can help:

• For whole home regulation, install a pressure reducing valve on your main water line and set it to 50-60 PSI.

• For tankless heaters, install a pressure relief valve and set to max 80 PSI.

• To eliminate water hammer, install water hammer arrestors near pipes.

According to the Washington Suburban Sanitary Commission, controlling water pressure to 50-60 PSI can reduce sediment and mineral buildup in your water heater by up to 50%.

When is it Time to Call a Professional?

While routine knocking noises can often be resolved with DIY maintenance, it‘s best to call in a professional hot water heater technician if:

• Knocking persists after you‘ve flushed the tank and secured fittings.

• Your tank shows signs of significant mineral scale, corrosion, or sediment buildup.

• Components need replacement and you are unsure how.

• You find cracks, leaks, or serious damage to the tank itself.

If your water heater is over 8-10 years old, it may be time to replace the entire unit if it is suffering from excessive sediment or mineral buildup. A technician can assess replacement options.

Preventative Maintenance is Crucial!

Routine maintenance is the best way to maximize your water heater‘s lifespan and prevent sediment buildup in the first place:

• Drain and flush the tank annually.

• Replace the anode rod every 3-4 years.

• Keep home water pressure around 50-60 PSI.

• Follow the manufacturer‘s maintenance guidelines.

According to the US Department of Energy, flushing your water heater annually can increase its efficiency by up to 4%.

Practice Safety When Working on Your Water Heater

Working on a hot water tank involves dealing with electricity, gas, and hot water. Take proper precautions:

• Turn off power and gas to tank before any maintenance.

• Allow hot tank to fully cool before draining water.

• Direct hot water away from yourself when flushing.

• Have a fire extinguisher on hand in case of accidents.

• Use caution when working inside the tank. Wear eye protection.

Let‘s Stop That Knocking For Good

Now you should feel ready to diagnose the cause of your water heater‘s knocking and take action to stop it through maintenance and repairs. With some helpful troubleshooting tips and step-by-step guides, you can get your hot water heater humming along smoothly again. But for any issues you aren‘t comfortable handling yourself, consult a professional for assistance. Stay safe and let me know if you have any other home maintenance questions!