A water heater should operate quietly. If yours is making sounds — popping, crackling, rumbling, hissing, or ticking — it is trying to tell you something. The noises are not always cause for alarm, but they always mean something is happening inside the tank, and understanding what that something is helps you decide whether to call a plumber or monitor the situation.
This guide explains the most common noises water heaters make, what causes them, and what action you should take for each situation.
Popping and Crackling: Sediment Buildup
This is the most common noise homeowners report from their water heater. The sound comes from water trapped beneath a layer of accumulated sediment at the bottom of the tank. When the burner beneath the tank heats the sediment-covered water, steam bubbles form and collapse as they rise through the sediment layer — producing a popping or crackling sound not unlike boiling water in a pot with too much oil.
What is happening: Over time, dissolved minerals from hard water (common throughout the San Gabriel Valley) settle to the bottom of the tank. This sediment layer reduces the efficiency of heat transfer from the burner to the water, causes the tank bottom to overheat slightly, and creates the conditions for that popping sound.
How to address it: Drain and flush the tank. This involves connecting a garden hose to the drain valve at the bottom of the tank, running the hose to a floor drain or outside, and opening the drain valve while the tank is off. Allow several gallons to flush out until the water runs clear. If the water does not run clear after a few flushes, or if the tank has not been flushed in more than two years, call a plumber to perform a professional flush and inspect the tank interior.
Prevention: If you live in Glendora, Covina, San Dimas, or other SGV cities with hard water, flushing the tank annually prevents sediment from building up. A water softener is the permanent solution — it removes the dissolved minerals before they enter the tank. Western Rooter’s team can test your water hardness and recommend whether a water softener installation makes sense for your home.
Rumbling and Booming: Severe Sediment and Potential Scaling
A deep rumbling sound that travels through the walls is an advanced stage of sediment buildup. When the sediment layer is thick enough, the water beneath it superheats before boiling — producing larger, more energetic steam explosions that create the rumbling and booming you hear through the wall.
What is happening: The sediment has built up to the point where normal tank operation is compromised. The tank’s lower heating element or gas burner is working harder and overheating to achieve the same hot water output, and the water temperature fluctuations are more pronounced. This is not immediately dangerous, but it significantly accelerates tank wear and can lead to tank failure.
How to address it: Schedule a professional flushing service immediately. If the tank has not been flushed in several years, the sediment may be compacted and a simple drain-and-flush may not fully clear it. A plumber with equipment to pressure-flush the tank or perform partial tank cleaning can remove the compacted layer. If the tank is more than 10 years old and the sediment has caused visible signs of reduced heating performance or higher gas bills, consider replacement rather than investing in repairs on an aging unit.
Hissing or Sizzling: Active Leak or Water Dripping on Hot Surfaces
A hissing or sizzling sound typically means water is contacting a hot surface somewhere in or around the unit.
What is happening: Condensation is forming on the flue or on hot metal surfaces inside the combustion chamber. This is normal during the first few minutes of heating if the tank is cold and the room is humid, and it typically stops after a few minutes once the tank warms up. If it continues throughout the heating cycle, or if you hear sizzling at the burner, water may be entering the combustion chamber or dripping on the flue, which is a serious issue.
How to address it: If the hissing is brief at the start of the heating cycle and stops within five minutes, it is likely normal condensation and not a concern. If it persists or is accompanied by a smell of combustion gases, shut off the gas supply, do not use the hot water, and call a plumber immediately.
Ticking or Pinging: Thermal Expansion in Pipes
A ticking or pinging sound that comes from the pipes near the water heater — not the tank itself — is caused by thermal expansion. As water inside the pipes heats up, it expands and puts pressure on the pipe walls. The pressure causes the pipes to flex slightly against their supports, producing a rhythmic ticking sound.
What is happening: Copper and some plastic pipes expand when heated and contract when cooled. The tick is typically most audible when a long pipe run is involved or when the water heater first fires up after a period of no use. This is one of the most common plumbing sounds in Los Angeles homes and is rarely a problem in itself — though it can indicate that your pressure-reducing valve (PRV) on the main water supply may be set too high if it is accompanied by elevated water pressure throughout the house.
How to address it: If the ticking is occasional and only during heating cycles, it is normal and does not require action beyond checking that pipe supports are secure. If the ticking is constant or very loud, or if you have noticed high water pressure at your faucets, have a plumber check your PRV settings. The water line services team can assess whether your pressure is in the normal range and adjust the PRV if needed.
Squealing or Whistling: Faulty Temperature and Pressure Relief Valve
A high-pitched squealing or whistling that sounds like it is coming from the tank itself or from a pipe connection may originate at the temperature and pressure (T&P) relief valve. This valve is the safety device on the side of the water heater that releases water if the tank pressure or temperature exceeds safe limits.
What is happening: The T&P valve is designed to open slightly during heating cycles to release excess pressure. On some units, this small release of steam and water vapor produces a whistling sound. This is normal on most water heaters, but the valve should only whistle for brief periods. A valve that whistles continuously may be stuck partially open, which is a potential safety concern.
How to address it: Continuous whistling from the T&P valve means the valve is not sealing properly and may need replacement. This is a straightforward repair that a plumber can complete in under an hour. Do not ignore a continuously whistling T&P valve — it is your water heater’s primary pressure safety device, and if it fails entirely, the tank has no controlled way to release dangerous pressure buildup. Schedule a service call to have the T&P valve inspected and replaced if needed.
Knocking or Hammering: Water Hammer
A sharp knocking or hammering sound in the pipes when you turn off a faucet or valve — not when the water heater heats — is called water hammer. This occurs when fast-moving water in the pipes is stopped abruptly, causing a pressure wave that jolts the pipe against its supports.
What is happening: Water is heavy, and when it is moving at full velocity through the pipes and suddenly stopped (by closing a valve), the momentum of that water mass creates a pressure spike that reverberates through the pipe system. Over time, this can loosen pipe supports, damage valves, and cause leaks at joints. Water heater-related water hammer is most noticeable when the water heater’s tank fills for the first time after being drained, or when the system is refilled after repair work.
How to address it: Water hammer that occurs only rarely or only when refilling the system after a repair is typically not a concern and resolves as the air cushions in the pipes re-establish themselves. Recurring water hammer during normal use indicates the system lacks properly installed air chambers (vertical capped sections of pipe that cushion the pressure wave) or that existing air chambers have lost their air cushion due to waterlogging. A plumber can install arrestors or restore air chambers to eliminate the hammering.
Should You Repair or Replace?
A general rule that applies to most aging water heaters: if your unit is approaching 10 years old and you are paying for repairs, calculate whether the repair cost plus the remaining lifespan is worth more than simply replacing the unit with a new, more efficient model. Storage tank water heaters less than 10 years old with a sediment problem respond well to professional flushing. Units over 12 years old that are showing multiple failure signs — rust-colored hot water, rumbling sounds, frequent leaks at the drain valve, visible corrosion on the tank exterior — are usually better replaced than repaired.
If your water heater is making noises and you are unsure whether to act, a plumbing inspection from Western Rooter takes less than an hour and gives you a clear picture of whether repair or replacement makes more sense for your specific situation. We serve Glendora, San Dimas, Covina, Azusa, Pasadena, and surrounding San Gabriel Valley communities.
A plumber who performs an annual water heater inspection can catch early warning signs like corrosion on the tank exterior, a degrading anode rod, or minor leaks at the drain valve before they become emergencies. Schedule a maintenance visit with Western Rooter to extend the life of your current unit.
