Water Heater Making Noise? What Each Sound Means

A water heater that starts making sounds it did not make before is worth paying attention to. Some noises are harmless. Others indicate that the unit needs maintenance or is heading toward failure. Here is what the most common water heater sounds mean and what to do about them.

Popping or Rumbling

This is the most common noise complaint, and it almost always points to sediment buildup at the bottom of the tank. Over time, minerals from hard water - calcium and magnesium primarily - settle and accumulate at the base of the tank. When the heating element (electric) or burner (gas) fires, water trapped beneath the sediment boils and forces its way through, creating a popping or rumbling sound.

The fix is to flush the tank. Turn off the heater, connect a garden hose to the drain valve at the base of the unit, and drain the tank fully. Then open the cold water supply briefly to stir up any remaining sediment and drain again. This is standard annual maintenance. If the unit has never been flushed and is several years old, the sediment layer may be thick enough that flushing alone does not fully clear it.

Persistent popping after flushing, or very thick sediment, often signals that the tank is nearing the end of its useful life.

Hissing

Hissing - a continuous sound, not just when the heater fires - often indicates a small water leak. Check the pressure relief valve, the drain valve at the bottom, and all pipe connections at the top for drips. A hissing pressure relief valve may be releasing small amounts of water due to excessive pressure or a valve that has begun to fail.

If the hissing is only audible when the heater is actively heating, it may be normal thermal expansion - water expanding as it heats can create a mild hissing sound in some units. That said, an intermittent hiss is worth monitoring.

Knocking or Banging

Knocking sounds - especially when hot water has just been used - are often caused by thermal expansion in the pipes. As hot water flows through metal pipes, the pipes expand slightly and contract again as they cool. This movement against pipe hangers, joists, or wall framing creates a knocking or ticking noise.

This is not a water heater problem per se - it is a pipe issue. Adding cushioned pipe hangers or adjusting existing ones often reduces the sound.

If the knocking comes from inside the tank during heating, it may again be sediment or a failing heating element striking the tank wall.

Screeching or Whining

A high-pitched screeching or whining sound, usually during heating cycles, often points to a partly closed valve restricting water flow. Check all shutoff valves connected to the heater - both the cold water inlet at the top and any isolation valves on the output line. Make sure they are fully open.

A faulty inlet control valve can also cause this sound and may need replacement.

Ticking

A regular ticking sound during or just after heating is often just thermal expansion of the metal tank or pipes. It is generally harmless. If the ticking is loud, persistent, or accompanied by other symptoms, it is worth having a plumber take a look.

When to Call a Plumber

Get a professional involved if you hear hissing and find an active leak, the pressure relief valve is dripping or releasing water, the unit is more than 10 years old and making new sounds, flushing the tank did not resolve popping sounds and they are getting worse, or you hear any electrical burning smell alongside the noise from an electric water heater.

Sources and editorial notes

Prices and permit requirements vary by location, property, equipment, and scope. Treat price ranges as planning estimates and confirm current requirements with the relevant authority and contractor.

• US Department of Energy - Energy Saver
• US Consumer Product Safety Commission - home safety

Related guides

• Water Heater Maintenance: What Homeowners Should Do Each Year
• Why Is My Air Conditioner Making a Loud Noise?
• Water Heater Installation Cost Guide (Tank vs. Tankless)

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