Is your water heater making noise? It’s one of the most common calls we get — and the good news is that the specific sound your unit makes is a diagnostic clue, the same way an error code is. Water heaters aren’t silent, but they shouldn’t be loud either. Some noises are completely normal, some are a cheap DIY fix, and a few mean you should shut the unit off and pick up the phone.
This guide decodes every common water heater noise — popping, rumbling, screeching, humming, knocking, and more — for both tank and tankless units, and tells you exactly which is which.
Jump to Your Sound
Tank Water Heater
Tankless Water Heater
From our service techs: Across thousands of service calls throughout Washington, Oregon, and California, the sounds below are the ones we’re called out for most. We’ve noted which you can safely handle yourself and which need a professional — because on a gas or electric water heater, a few of these noises are genuine safety issues, not just annoyances.
Popping or Rumbling — Sediment Buildup
Schedule ServiceWhat it means: This is the #1 water heater noise, and it almost always means mineral sediment has built up on the bottom of your tank. When the burner fires, water trapped under the sediment layer boils and bursts through it — that’s the pop. A deep rumble is the same problem at a larger scale.
Why West Coast homeowners hear it more: Much of California and parts of Eastern Washington and Oregon have moderately hard to hard water. The harder your water, the faster sediment accumulates.
What to do: A tank flush usually solves it. If your tank is under ~8 years old and has been flushed regularly, this is routine maintenance — see our guide on flushing your tank. If the tank is 8–12+ years old and has never been flushed, flushing can occasionally reveal leaks the sediment was plugging — have a pro assess it first. Watch for the signs it’s time for replacement.
Ignore it and: Sediment insulates the water from the burner, so the unit runs longer, your gas bill climbs, and the tank bottom overheats — which shortens tank life significantly.
Field note: in hard-water areas like much of California, a popping or rumbling water heater making noise after every heating cycle is almost always sediment — and it’s the single most common noise complaint we see.
Screeching or Whistling — Restricted Water Flow
DIY Check FirstWhat it means: A high-pitched screech means water is being forced through a too-small opening. The usual suspects: a partially closed inlet valve, a partially closed outlet valve, or a temperature & pressure (T&P) relief valve that’s opening because tank pressure is too high.
What to do: Check that the cold water inlet valve on top of the unit is fully open. If the sound is coming from the T&P valve on the side of the tank, that’s a safety valve doing its job under excess pressure — call a pro. Don’t cap, plug, or ignore a whistling T&P valve.
Sizzling or Hissing — Moisture Meeting Heat
Call a ProWhat it means: On gas units, sizzling is usually water contacting hot surfaces. Two very different causes: (1) condensation dripping onto the burner — normal for a few minutes after a cold tank refills, especially in winter; (2) a leak dripping onto the burner or hot exterior — not normal, ever.
What to do: If the sizzling stops shortly after the unit finishes heating, it’s likely condensation. If it persists, or you see any moisture around the base, turn the unit off and call a pro — start with our water heater leaking guide.
Humming — Electric Element Vibration
DIY FixWhat it means: Electric tank models only. Cold water flowing around the heating element makes it vibrate in its bracket — like a tuning fork.
What to do: This one is harmless and has a satisfying fix: tightening the element a quarter-turn usually stops the hum. If you’re not comfortable working on an electric water heater (power must be off at the breaker), it’s a quick job for a technician — here’s how to troubleshoot an electric water heater.
Knocking or Banging in the Walls — Water Hammer
DIY / Call a ProWhat it means: If the banging happens when a tap, dishwasher, or washing machine shuts off — and seems to come from the pipes, not the tank — that’s water hammer: moving water slamming to a stop and shaking the pipes.
What to do: Not dangerous to the water heater itself but hard on plumbing joints over time. A plumber can add a water hammer arrestor. If your home has a closed system, this is also a sign you may need a thermal expansion tank.
Ticking — Pressure & Temperature Changes
Usually NormalWhat it means: Rhythmic ticking is usually the heat trap nipples (one-way valves on the water connections) or hot water pipes expanding and contracting against wood framing as temperature changes.
What to do: Usually nothing. If it drives you crazy, a technician can swap heat trap nipples for standard dielectric ones, or pipes can be re-secured with cushioned clamps.
Crackling — Condensation on the Burner
Usually NormalWhat it means: On gas units, light crackling right after a heating cycle starts is typically condensation burning off the burner assembly. Common in cold weather and after heavy hot water use.
What to do: If it fades as the unit heats, it’s normal. If crackling is constant or paired with soot, yellow flame, or an error code, have the combustion system inspected — see our water heater error codes guide.
Tankless Water Heater Sounds
Tankless units have fans, valves, and igniters, so they’re naturally more “talkative” than tanks. Here’s what’s normal and what isn’t:
That’s the igniter firing and flow-sensor valves opening when you turn on a hot tap. No action needed.
The exhaust fan purges combustion gases for a minute or two after heating stops.
Often a loose screw, panel, or mounting bracket — or pipes vibrating against framing. If tightening accessible hardware doesn’t fix it, scale buildup on internal components may be the cause, and it’s time for a descaling flush. See our tankless maintenance steps.
This is delayed ignition — gas accumulating before it lights. Causes include a dirty burner, misadjusted gas pressure, or venting problems. Stop using the unit and call our tankless repair service.
On condensing models, this usually means the condensate drain line is clogged or improperly sloped. Left alone, acidic condensate backs up into the unit.
Can indicate a gas supply issue, air in the gas line, or restricted airflow — all combustion-related, none DIY.
Tip: If your tankless unit is making noise and showing a code on its display, the code is the faster diagnostic. See our complete water heater error codes guide.
Quick Reference Table — Every Sound
| Sound | Unit type | Likely cause | Verdict |
|---|---|---|---|
| Popping / rumbling | Tank | Sediment buildup | Schedule a flush |
| Screeching | Both | Restricted flow / partially closed valve | Check valves; call pro if T&P |
| Sizzling / hissing | Tank (gas) | Condensation or a leak | Call pro if persistent |
| Humming | Tank (electric) | Loose heating element | Tighten element |
| Knocking in walls | Both | Water hammer | Add arrestor / expansion tank |
| Ticking | Tank | Heat traps / pipe expansion | Normal |
| Crackling | Tank (gas) | Condensation on burner | Normal if it fades |
| Clicking at startup | Tankless | Igniter / valves | Normal |
| Fan after shutdown | Tankless | Exhaust purge | Normal |
| Rattling | Tankless | Loose hardware or scale | Tighten; descale if persists |
| Boom at ignition | Tankless | Delayed ignition | Call pro — stop using unit |
| Gurgling | Tankless | Clogged condensate drain | Call pro |
| Whistling | Tankless | Gas / air supply issue | Call pro |
When a Noise Means Replacement, Not Repair
A noise alone almost never means your water heater is done. But rumbling plus any of these usually does: the unit is 10+ years old, you see rusty water from hot taps, or there’s moisture around the base. In that case, compare repair cost against replacement before sinking money into an old tank — here’s a breakdown of water heater replacement cost.
Frequently Asked Questions
Is a noisy water heater dangerous?
A water heater making noise is usually not an immediate danger — most sounds are sediment or flow-related. The exceptions: a whistling T&P relief valve (pressure problem), persistent sizzling (possible leak), and a booming ignition on tankless units (delayed ignition). Treat those three as urgent.
Why does my water heater pop only at night?
It pops whenever the burner runs. You notice it at night because the house is quiet and the unit often reheats after evening showers and dishwasher cycles.
Will flushing my water heater stop the popping?
In most cases, yes — flushing removes the sediment that causes the sound. If the tank is old and heavily scaled, one flush may not remove hardened sediment, and repeated noise afterward suggests the tank is near end of life.
Is it normal for a tankless water heater to click?
Yes. Clicking when you open a hot tap is the igniter and valves operating normally. Booming, whistling, or gurgling are the tankless sounds that warrant a service call.
How often should I flush my water heater on the West Coast?
Once a year is the safe default. In hard-water areas (much of California, parts of Eastern WA/OR), consider every 6–12 months for tanks and an annual descaling flush for tankless units.
Still Hearing It?
If you’ve checked the valves and the sound persists — or you’re hearing one of the “call a pro” sounds above — we can diagnose it fast. We service all major brands throughout Washington, Oregon, and California (Bay Area & Southern California).
Call before noon for same-day service in most of our service areas.
