Why Is My Water Heater Making Noise? A Boise Plumber Explains

If your water heater is making strange noises, you’re right to be concerned—but don’t panic. Most water heater sounds have identifiable causes, and many can be resolved without replacing the unit. As Boise plumbers, we hear about noisy water heaters constantly, and Boise’s hard water is the underlying culprit in the majority of cases. This guide explains the six most common water heater noises, what causes each one, when it’s dangerous versus harmless, and what to do about it.

The 6 Most Common Water Heater Noises

1. Popping

Sounds like: Popcorn popping, crackling, or small snapping sounds

Cause: This is the most common water heater noise in Boise homes. When Boise’s hard water (8–12 grains per gallon) is heated, dissolved calcium and magnesium minerals precipitate out and settle on the bottom of the tank as sediment. Over time, this sediment layer traps small pockets of water beneath it. When the burner heats the tank bottom, these trapped water pockets flash to steam, creating popping sounds as the steam bubbles escape through the sediment.

Is it dangerous? No, popping itself isn’t dangerous. However, it indicates significant sediment buildup, which reduces your water heater’s efficiency by 25–30% and accelerates tank deterioration. Left unaddressed, heavy sediment can lead to premature tank failure.

Fix: Flush the water heater to remove sediment (see DIY flush steps below). If popping has been occurring for years without maintenance, a professional flush may be needed—hardened sediment (calcified scale) may not drain through the valve.

2. Rumbling

Sounds like: A low, continuous rumbling or boiling sound

Cause: Rumbling indicates a thick layer of sediment on the tank bottom. It’s essentially a more advanced version of popping. The entire sediment layer shifts and churns as water circulates beneath and through it during heating cycles. In Boise, where hard water accelerates sediment accumulation, rumbling can develop within 3–5 years without regular flushing.

Is it dangerous? Rumbling is a warning sign of significant sediment buildup. While not immediately dangerous, it means your water heater is working much harder than it should, wasting energy and shortening the tank’s lifespan. In extreme cases, the sediment can insulate the tank bottom from the water above, causing the steel at the bottom to overheat and weaken.

Fix: Flush the tank. If the rumbling has been present for a long time, the sediment may be calcified and difficult to flush—a plumber can perform a more thorough cleaning. If the water heater is more than 10 years old and rumbling, it may be more cost-effective to replace it.

3. Screeching or Whistling

Sounds like: A high-pitched screech, whistle, or squeal

Cause: This sound almost always comes from a valve—typically the temperature and pressure (T&P) relief valve or an inlet/outlet valve that isn’t fully open. Water forced through a restricted opening creates a whistling effect, similar to a tea kettle. Scale buildup from Boise’s hard water can partially clog valves, creating this restriction.

Is it dangerous? Potentially. If the T&P relief valve is screeching, it may be releasing pressure because the tank’s pressure or temperature is too high. This is a safety concern. If the sound comes from a supply valve, it’s less urgent but should still be addressed to prevent valve failure.

Fix: First, check that all valves on and near the water heater are fully open. If the sound comes from the T&P valve, do not cap it or try to stop it from releasing. Call a plumber—the valve may need replacement, or the water heater may have a more serious pressure or temperature control issue.

4. Ticking

Sounds like: A rhythmic ticking or clicking, similar to a clock

Cause: Ticking is usually caused by heat traps—small check valves installed at the hot and cold water connections on top of the water heater. Heat traps prevent heat loss by stopping hot water from naturally convecting up into the cold water line. As they open and close, they produce a ticking sound. This is a normal operating sound in many newer water heaters.

Is it dangerous? No. This is a normal operating sound. Heat traps improve energy efficiency and are a standard feature on modern water heaters.

Fix: No fix is needed—this is normal. If the ticking is bothersome, a plumber can replace the heat trap nipples with dielectric nipples, which are silent. However, you’ll lose the small energy-saving benefit of the heat traps.

5. Humming

Sounds like: A steady, low-frequency hum or vibration

Cause: This noise is specific to electric water heaters. It’s caused by the heating element vibrating as electric current flows through it. The vibration is transmitted to the water and the tank, creating an audible hum. A loose element can amplify the sound.

Is it dangerous? No. Humming is harmless and typically just annoying. However, a very loud hum or a change in the humming pattern could indicate a failing element.

Fix: Slightly tightening the heating element can reduce the vibration. If the humming is new or has changed, have a plumber inspect the element—it may be scaled over or starting to fail. Learn more about element issues on our water heater repair page.

6. Crackling or Sizzling (Gas Water Heaters)

Sounds like: Crackling, sizzling, or hissing from the bottom of the unit

Cause: Condensation. When cold water enters a gas water heater (remember, Boise’s incoming water is around 45°F in winter), condensation forms on the outside of the cold tank and drips onto the hot gas burner below. The water droplets sizzle on contact with the burner, creating crackling or sizzling sounds. This is most noticeable during heavy hot water use or after the tank has been refilled (after a flush or heavy draw).

Is it dangerous? No. Condensation sizzling on the burner is normal, especially in cold weather when incoming water temperature is lowest. It typically stops once the tank heats up and condensation decreases.

Fix: No fix needed—this is normal operating behavior. If the sizzling is constant and accompanied by water pooling at the base of the heater, check for a tank leak rather than condensation.

How Boise’s Hard Water Causes Water Heater Noise

Boise’s hard water (8–12 GPG) is the primary driver behind the most common water heater noises—popping and rumbling. Here’s the cycle:

1. Hard water enters your water heater
2. As the water heats, dissolved minerals (calcium carbonate) come out of solution
3. These minerals settle to the bottom of the tank as white, chalky sediment
4. The sediment layer grows thicker with each heating cycle
5. Within 1–3 years in Boise (without flushing), the sediment layer is thick enough to trap water and cause popping sounds
6. Left longer, the sediment hardens (calcifies) and becomes much harder to remove

This process happens faster in Boise than in cities with softer water. Where a homeowner in Portland (soft water) might go 3–5 years before noticing sediment issues, a Boise homeowner can experience them within 1–2 years.

DIY Water Heater Flush: Step-by-Step

Regular flushing is the best way to prevent sediment-related noises and extend your water heater’s life. Here’s how to flush a standard tank water heater:

1. Turn off the heat source. For gas: set the thermostat to “pilot.” For electric: turn off the breaker at your electrical panel.
2. Connect a garden hose to the drain valve at the bottom of the tank. Run the hose to a floor drain, outside, or into buckets.
3. Open a hot water faucet somewhere in your home (a nearby sink works). This allows air into the system and helps the tank drain.
4. Open the drain valve. Let the water flow until it runs clear. Initially, you’ll likely see cloudy or sediment-filled water—this is normal and confirms the flush is working.
5. Close the drain valve once the water runs clear (typically 5–15 minutes).
6. Close the hot water faucet you opened earlier.
7. Turn the heat source back on. For gas: reset the thermostat to your normal setting (120°F recommended). For electric: flip the breaker back on.
8. Wait 30 minutes and test a hot water faucet to confirm the system is working properly.

Important: The water coming out will be very hot. Use caution and keep children and pets away during the flush. If the drain valve is stuck or you’re uncomfortable with the process, call a professional.

Maintenance Schedule to Prevent Noise

Given Boise’s hard water, we recommend this maintenance schedule:

• Every 6–12 months: Flush the tank to remove sediment
• Every 2–3 years: Inspect and test the T&P relief valve; inspect the anode rod
• Every 3–5 years: Replace the anode rod (the “sacrificial” rod that protects the tank from corrosion)
• Every 10–15 years: Plan for water heater replacement (tank models)

When to Call a Plumber

Call a professional if you experience any of these situations:

• The T&P relief valve is repeatedly discharging water or steam
• You smell gas near a gas water heater
• The water heater is leaking from the tank itself (not just condensation)
• Strange noises are accompanied by discolored (rusty) hot water
• The unit is more than 12 years old and making new noises
• You’re unable to flush the tank (valve is stuck or sediment won’t drain)
• Any noise that’s sudden, loud, or sounds like knocking or banging (this could indicate a dangerous pressure buildup)

Frequently Asked Questions

Is a popping water heater dangerous?

A popping water heater is not immediately dangerous—the sound is caused by steam bubbles escaping through sediment at the bottom of the tank. However, it indicates significant sediment buildup that reduces efficiency and shortens the tank’s lifespan. If the popping is accompanied by very hot water (above 120°F at the faucet), leaking, or a constantly running burner, call a plumber for inspection.

How often should I flush my water heater in Boise?

Due to Boise’s hard water (8–12 GPG), we recommend flushing your water heater every 6–12 months. Homes with very hard water or high water usage should flush more frequently. If you have a water softener, annual flushing is usually sufficient. Regular flushing prevents sediment buildup, reduces noise, maintains efficiency, and extends the life of your water heater by several years.

Why does my water heater make noise only at night?

Water heaters often seem louder at night because your home is quieter—the sounds were always there but were masked by daytime activity. Additionally, if your thermostat has a setback program or you use less hot water in the evening, the tank may go through a longer heating cycle at night, making sediment-related sounds more noticeable. The fix is the same—regular flushing to reduce sediment.

Can I fix a noisy water heater myself?

In many cases, yes. Flushing the tank to remove sediment is a straightforward DIY project for most homeowners and resolves popping and rumbling sounds in most cases. For ticking (heat traps) and crackling (condensation), no fix is needed—these are normal. However, screeching valves, persistent humming, and any noise accompanied by leaking, unusual odors, or temperature problems should be diagnosed by a professional plumber.

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Is your water heater making unusual noises? Hyde Park Plumbing’s licensed technicians diagnose and repair all types of water heater problems throughout the Boise metro area. Call us at (208) 994-3745 for professional diagnosis and repair—we’ll tell you honestly whether your unit needs a simple flush or it’s time for a replacement.