What Those Noises From Your Water Heater Mean

Water heaters are supposed to be boring. When one starts making noise, the sound tells you a lot about what is happening inside.

Popping, rumbling, or crackling

This is the one, by a wide margin. It sounds like a kettle full of gravel.

Cause: sediment on the bottom of the tank. Minerals settle out of the water and build a layer at the bottom. On a gas heater the burner is directly under that layer, so you are heating through a crust of scale. Water trapped underneath flashes to steam and forces its way up through the sediment, and that is the popping.

Beyond the noise, it costs you. That layer insulates the water from the burner, so the heater works harder for the same hot water. It also drives the steel at the bottom of the tank hotter than it was designed to run, which shortens the tank’s life.

New Hampshire well water tends to be harder than average, which is why we see this a lot here.

The fix: flushing. Done regularly, once a year, it is straightforward maintenance and it works. Done for the first time on a ten year old heater that has never been touched, it is riskier. The drain valve on an old tank can be scaled shut, and opening it can leave you unable to close it. On a heater that far gone, sometimes the honest advice is to leave it alone and plan on replacement.

If yours is newer and has never been flushed, start doing it. If yours is old and loud, get somebody to look at it before you open a valve you cannot close.

High pitched whine or singing

Usually restricted flow somewhere. A partially closed valve, a failing pressure reducing valve, sometimes sediment in the outlet.

Not typically an emergency, but worth looking at, because whatever is restricting flow is also affecting the rest of the plumbing.

Ticking or light tapping

Often just thermal expansion, metal moving as it heats and cools. Common right after a draw. On heaters with heat trap nipples it can be normal.

Generally nothing.

Hissing or sizzling

This one gets your attention. Sizzling usually means water hitting something hot that it should not be touching. That means a leak, either from the tank or from a fitting, dripping onto the burner assembly or onto the elements.

Shut it off and get somebody out. A leaking tank does not get better and can fail suddenly, and a tank failure means a lot of water in your basement all at once.

Banging in the pipes, not the heater

If the bang happens right when a faucet or an appliance shuts off, that is water hammer, not the water heater. A valve closes fast, moving water has nowhere to go, and the shock travels through the pipe.

Fixed with arrestors, or sometimes by recharging air chambers if the house has them. Worth solving because the repeated shock is hard on joints and on appliance valves.

Rotten egg smell instead of a noise

Different problem, same appliance. Usually a reaction between the anode rod and sulfate in the water, most often on wells. It gets addressed by changing the anode rod type. Do not just pull the rod out, it is what protects the tank from corrosion.

Preventive work that actually pays

Flush annually. Especially on hard water.

Check the anode rod every few years. It is a sacrificial metal rod that corrodes so the tank does not. Once it is consumed, the tank starts corroding. Replacing a rod is far cheaper than replacing a heater, and almost nobody does it. On hard water it may need attention every three to five years.

Test the temperature and pressure relief valve annually. Lift the lever, confirm water discharges, confirm it reseats. That valve is the safety device on a pressure vessel full of very hot water. If it is crusted shut, replace it.

Set the thermostat to 120. Hot enough for household use, cool enough to reduce scald risk and slow scale buildup.

Lifespan

Typical tank heater runs eight to twelve years. Hard water shortens that, good maintenance extends it.

If yours is past ten, sitting in a finished space, and starting to make noise, start thinking about replacing it deliberately rather than waiting for it to let go on a Sunday. A pan and a drain under it are cheap insurance in the meantime.