Normal and Not-Normal Sounds from Your Water Heater
Why this matters
A tank water heater is a large vessel of hot water under the same pressure as the rest of your plumbing, sitting in a closet or basement you rarely visit. Most of the sounds it makes are signs of ordinary aging. A few are the heater protecting itself, and you need to recognize those, because the right response is the opposite of what feels natural. This card sorts the sounds and the drips into three groups: normal, call a plumber, and leave the house.
Three signs that come before any listening
A rotten-egg or sulfur smell near a gas water heater. Natural gas and propane carry an added odor that smells like rotten eggs. Do not turn the gas control, flip a light switch, unplug anything or use your phone in the house. Get everyone out, leave the door open behind you, and call the gas utility or 911 from outside and well away from the house. See How to Respond If You Smell Gas in Your Home.
Hot water or steam coming out of the relief valve pipe. Every tank has a temperature and pressure relief valve, usually called the T&P valve: a brass valve near the top of the tank with a pipe running down toward the floor. It opens when the tank gets too hot or the pressure too high. If it is gushing hot water or steam, stay clear of the pipe's outlet (that water can scald). Turn off the heat source: for a gas heater, turn the gas control knob to OFF; for an electric heater, switch off its breaker at the panel, but only if the floor between you and the panel is dry. Then close the cold-water valve on the pipe entering the top of the tank and call a plumber. Leave the heat off and the valve closed until the plumber has found why the valve opened; the plumber is the one who turns it back on. Never cap, plug or tie off the relief pipe. It is the part that stops a tank from rupturing.
Water spreading toward electrical equipment or outlets. Stay out of standing water that is near outlets, the heater's own wiring, or a furnace. Shut off power at the panel only if you can reach it on dry floor; otherwise wait for the plumber or an electrician. Once it is off, it stays off until the leak is stopped and an electrician or the plumber says the area is dry and safe. See How to Handle the First Ten Minutes of a Water Leak.
The normal sounds of an aging tank
Popping, crackling or rumbling while it heats. This is the classic water heater noise, and it comes from sediment. Minerals in your water settle to the bottom of the tank as a crusty layer. Water trapped under that layer gets heated past boiling, turns to small steam bubbles, and the bubbles collapse with a pop as they rise into cooler water. It is the same physics as a kettle rumbling before it boils. It does not mean the tank is about to burst. It does mean the heater is working harder: the sediment insulates the water from the burner or bottom element, so heating takes longer and the tank bottom runs hotter. Hard water areas see it within a few years.
A short hiss or sizzle on a gas heater right after a lot of hot water is used. When the tank refills with cold water, moisture from combustion condenses on the cold tank surface and drips onto the burner, where it sizzles. It is normal for a few minutes after a big draw, and it should stop as the tank warms up. Constant sizzling with water collecting under the heater is not condensation; see the dry-check below.
Ticking or tapping in the pipes. Copper and plastic pipes expand as hot water flows and shrink as they cool, and they tick where they rub against a strap or a joist. Harmless.
A faint hum on an electric heater. Heating elements can hum slightly while they are on.
A soft whine or whistle while water runs. Usually a valve that is partly closed, often the cold-water valve at the top of the tank. It points to a valve, not to the heater.
Sounds and signs that mean call a plumber
- Loud, frequent banging that started recently. Heavy sediment, or water hammer in the pipes (a bang when a faucet or washer valve shuts quickly). High house water pressure makes both worse.
- The T&P valve dripping or trickling now and then. Not gushing, just a wet pipe end or a small puddle after hot water use. That is the valve reacting to something: high pressure, pressure spikes as water heats, or a valve that is simply worn. A dripping relief valve is a symptom; replacing the valve alone often fixes nothing.
- Water under the tank that is not condensation. The tank body itself leaking is the end of the heater's life. Tanks fail from the inside out once the lining and the protective rod inside are used up.
- Rusty or discolored hot water only. If cold water is clear and hot is not, the tank interior may be corroding.
- Hot water that smells like rotten eggs at the faucet, but no smell in the air around the heater. This is usually not gas. Bacteria in some water supplies react with the metal rod inside the tank and produce a sulfur smell in the hot water. It is a nuisance, not an emergency. If you smell it in the air near a gas heater, though, treat it as gas and go back to the top of this card. When in doubt, you treat it as gas.
The puddle case, worked through
What happened. A homeowner has a 50-gallon gas water heater in the basement. The label (see Reading the Label on Your Water Heater) puts its manufacture date eleven years ago. It has been rumbling for about two winters. One Saturday there is a damp spot on the floor about the size of a dinner plate beside the tank. There is no gas smell and nothing is gushing.
The first move is a dry-check, not a guess. The question is where the water starts, and a puddle on the floor hides that, because water runs along the tank and pools at the low point. So they:
- Wiped the floor and the outside of the tank dry with a towel.
- Laid dry paper towels in four places: under the end of the T&P relief pipe, under the drain valve near the bottom of the tank, around the base of the tank, and on top of the tank around the two pipe connections.
- Ran a long shower and the dishwasher, then checked the towels two hours later, and again the next morning.
What the towels showed.
| Paper towel at | 2 hours later | Next morning |
|---|---|---|
| T&P relief pipe outlet | Soaked | Soaked again |
| Drain valve | Dry | Dry |
| Base of tank | Damp only where water ran over from the T&P towel | Same |
| Top connections | Dry | Dry |
What that means. The tank is not leaking. The water is coming from the relief valve, and it comes after hot water use. In this case they also screwed an inexpensive pressure gauge onto an outdoor hose faucet (see The Water Pressure in Your House and the Valve That Controls It), and it read 95 psi with nothing running in the house. That is above the 80 psi most plumbing codes cap static pressure at, so the relief valve was doing its job against pressure that was too high, made worse each time the tank heated cold water and that water expanded.
What they told the plumber. "50-gallon gas heater, eleven years old. The T&P pipe drips after hot water use; the tank body and fittings are dry on a towel check. A hose-bib gauge reads 95 psi static. It has rumbled for two winters." That one message gives the plumber three separate things to bring: a fix for the house pressure, a look at the expansion tank (a small tank on the cold line that absorbs the water's expansion, if the home has one), and an honest conversation about an eleven-year-old tank with heavy sediment.
What would have changed the answer. If the towel at the base of the tank had been soaked while the T&P towel stayed dry, with rust stains on the bottom of the tank jacket, the tank itself is leaking. In that case: turn the gas control to OFF (or switch off the breaker for an electric heater, from dry floor), close the cold-water valve at the top of the tank, and call the plumber about replacement. The heater stays off until the plumber has replaced it. Draining a hot tank yourself risks scalding and flooding, so leave that to the plumber unless your plumber walks you through it. If the towels had all stayed dry, the first damp spot was probably condensation after a big draw, which is normal and stops once the tank warms.
The failure mode to avoid. The common mistake with a dripping relief valve is to treat the drip as the problem: putting a bucket under it and forgetting it, or worse, capping the pipe. A capped relief pipe removes the one thing standing between a pressure problem and a tank failure. The drip is the heater telling you something about pressure or temperature.
Temperature, and why it shows up in sounds
A tank set very hot rumbles more, because the bottom runs hotter and sediment hardens faster, and it raises the scald risk at every faucet. Many plumbers and safety groups suggest around 120 F at the tap as a starting point that balances scald risk and comfort. Some households (an immune-compromised family member, for instance) are advised differently by their doctor or plumber. See How to Check Your Hot Water Temperature at the Tap for doing that without touching the heater's controls.
Your part, and where it ends
Your part: listen, run the paper-towel dry-check, read the label, check house pressure with a hose-bib gauge, keep the area around the heater clear (see How to Keep the Space Around Your Furnace and Water Heater Safe), and know where the gas control, the breaker and the cold-water valve are (see Your Home's Shutoffs: Water, Gas and Electric).
The plumber's part: anything inside the burner compartment or electrical covers, the gas line, the T&P valve, the expansion tank, adjusting house pressure, flushing an old tank that has never been flushed (an old drain valve may not close again once opened), and replacement. Some owner's manuals describe a yearly flush you can do on a newer heater. Follow your own manual for that, and if it has been years since the last one, let the plumber do the first flush.
References
- See related: How to Respond If You Smell Gas in Your Home
- See related: The Water Pressure in Your House and the Valve That Controls It
- See related: Reading the Label on Your Water Heater
- See related: Living with Your New Water Heater
- Your water heater's owner's manual for the relief valve, flushing schedule and temperature setting specific to your model