Why Does Your water heater is making a knocking noise?
A knocking noise comes from a water heater is a common issue that many users experience. Although it might seem harmless, it often signals an underlying problem that could lead to reduced efficiency or more serious damage if left unaddressed. Water heater is making a knocking noise is usually a sign of sediment buildup, overheating of water heater, or thermal expansion within your water heater. Understanding the cause can help you quickly solve this issue and prevent further damage.
What causes the water heater is making a knocking noise?
Sediment Buildup: The most common reason of water heater is making a knocking noise, the formation of sediment buildup at the bottom of the water heater tank. Hard water’s minerals such as Calcium and Magnesium accumulate inside the water heater tank. This layer of sediment buildup work as wall between the heating element and the water. Due to that the heater uses more energy to get required temperature. When the heater operates, the sediment traps small amounts of water. As the water heats and turns to steam, it creates pressure, causing the popping or knocking sound. It also reduces the efficiency of the water heater and increases energy costs.
Overheating of Water Heater:
Another reason for water heater is making a knocking noise could be overheating. If the thermostat on the water heater is malfunctioning or set too high, it can cause the water inside the tank to reach temperatures that are excessively high. When the water temperature exceeds the safe limits, it can result in steam pockets forming within the tank. These pockets can cause pressure fluctuations, leading to the hitting and knocking sounds. In severe water heater is making a knocking noise cases, the tank may be at risk of burst if the pressure becomes too high, and overheating can also damage the internal components of the water heater.
So, it is important to ensure the thermostat is correctly calibrated and the water temperature is set between 120 and 140 degrees Fahrenheit.
Thermal Expansion and Its Effect on Water Heater Noise
When water is heated, it naturally expands. This is a basic principle of thermodynamics. As water molecules heat up, they move faster and take up more space, causing the water to increase in volume. In a water heater, this process is especially noticeable when the tank cycles on to heat cold water or off once the desired temperature is reached. The problem arises when the expansion of the heated water has nowhere to go.
If the water heater’s plumbing system does not have an expansion tank, or if the expansion tank fails, the pressure caused by the expanding water can cause substantial stress on the pipes. This added pressure builds up and can cause the pipes to shift, bend, or vibrate as they try to accommodate the extra volume of water. These shifting pipes can create water heater is making a knocking noise or banging sounds that users often hear when the water heater is running.
An expansion tank absorb this increased pressure and give the water a place to expand into without stressing the pipes. Without a properly functioning expansion tank, the pressure from thermal expansion can reach levels that cause the pipes to rattle against the walls of the house, making loud noises, particularly when the water heater starts up or shuts off. In extreme cases, the stress from constant thermal expansion can even cause leaks or damage to the plumbing system over time.
Why Should You “water heater is making a knocking noise” Address It?
Ignoring the knocking sound can lead to more significant issues:
Reduced efficiency: Sediment accumulation makes the heater work harder, increasing energy expenses.
Shortened lifespan: Over time, sediment or pressure issues can damage the tank, requiring costly repairs or replacements.
Potential leaks: Extreme pressure from thermal expansion or water hammer can eventually cause pipes to burst or the tank to leak.

How to Fix “water heater is making a knocking noise”
Flush the Tank:
Regularly cleaning your water heater can help avoid sediment accumulation.
Cut off the water inflow, gas supply, and electricity.
Connect a pipe to extract water directly to the drain.
To let the water and sediment go, open the valve.
Close the valve, replenish the tank, and then restart the heater.
Install a hydraulic shock absorber: A hydraulic shock absorber absorbs shockwaves in pipes, preventing hitting noise. Installing this straightforward remedy is easy for a plumber.
Add & Check the Expansion Tank: If thermal expansion is the problem, ensure your system has a properly functioning expansion tank. This tank absorbs the pressure created by expanding water, protecting your pipes and reducing noise.
Installing an ion exchange unit: An ion exchange device can be installed to fix your hardness concern. Hard water’s minerals are successfully removed by the gadget. It will also reduce substances in the water, reduce knocking sound, and prolong the water heater’s lifespan.

Tips to Prevent Future Knocking Noises
Regular Maintenance: To avoid sediment buildup, flush your water heater at least once a year.
Slowly Close Valves: Avoid sudden changes in water flow to minimize water hammer.
Inspect Components: Regularly check the expansion tank and other system components for wear or damage. The knocking sound from water heater can be alarming, understanding its possible causes is the first step in addressing the issue. Whether it’s sediment buildup, overheating, or expansion, timely attention can help prevent more severe problems. Regular maintenance, such as flushing the tank to remove sediment and checking the temperature settings, can ensure that the water heater operates efficiently and quietly.
If the noise persists, consulting a professional plumber would be the first priority to identify and resolve the issue before it leads to more costly repairs. In the long run, proactive care to the water heater will extend the longevity and keep the hot water running smoothly.