Water heater making noise: what each sound is telling you

Water heaters are supposed to be close to silent. When one starts making noise it is generally telling you something specific, and the sound narrows it down quickly.

Popping, rumbling or a sound like boiling gravel

This is sediment, and it is the most common noise complaint we get in Iowa. Hard water deposits minerals on the bottom of the tank, and over the years that builds into a crusty layer. On a gas heater the burner is underneath, so it is now firing through an insulating crust. Water gets trapped beneath the sediment, turns to steam, and forces its way up through it - that is the popping.

What it costs you: the burner works harder for the same hot water, the tank holds less usable volume, and the steel at the bottom runs hotter than it was designed to, which shortens the life of the tank.

What to do: flush the tank. On a heater that has been flushed regularly this is routine maintenance. On a ten year old tank that has never been flushed, the sediment can be solid enough that flushing dislodges very little, and disturbing it sometimes reveals corrosion that the sediment was effectively plugging. We will tell you honestly which situation yours is in before starting.

If the tank is under about eight years old, this is a repair job and worth doing. Past twelve, a noisy tank is often telling you to plan a replacement before it decides for you.

Ticking or tapping

Usually harmless. It is normally thermal expansion - metal pipes expanding as hot water moves through them and contracting as they cool, tapping against a joist or a strap. Heat trap nipples in the heater's connections make a similar sound.

If the ticking is new and rhythmic and coincides with the heater firing, it is worth a look, but on its own this rarely indicates a fault.

Screeching or a high whistle

Water forcing through a restriction. Check that the inlet and outlet valves are fully open - a partially closed valve is the usual cause and the easiest fix. If a temperature and pressure relief valve is whistling, that is different and more urgent: it means the valve is venting, which points at excessive pressure or temperature in the tank.

A T&P valve that is discharging should never be ignored or capped. It is the safety device that stops a water heater becoming dangerous. Call someone.

Hammering or banging when a tap shuts off

This is water hammer and it is a plumbing system problem rather than a heater problem. Fast-closing valves - washing machine solenoids especially - stop moving water abruptly and the shock travels through the pipes. It is fixable with arrestors, and it is worth fixing because repeated shock loosens joints over time.

Humming

On an electric heater, usually the upper element vibrating in the water flow. Tightening it normally stops it. Harmless, but easy to sort out.

Crackling or sizzling on a gas heater

If it comes from underneath the tank, it can be condensation dripping onto the burner, which is normal on a cold start. If it is persistent and there is water pooling under the heater, that is a different matter - a leaking tank cannot be repaired, and the sizzling is water hitting the burner assembly.

Water at the base of a heater always deserves a call. Distinguish between a fitting dripping, which is a repair, and the tank body seeping, which is the end of that heater.

The maintenance that prevents most of this

• Flush the tank annually. In hard water areas, which is most of Iowa, this matters more than most homeowners realise.
• Check the anode rod every few years. It is a sacrificial magnesium or aluminium rod that corrodes so the tank does not. Once it is consumed, the tank starts.
• Test the T&P valve occasionally by lifting the lever and letting it snap back.
• Consider a water softener if you are on hard water. It is the single most effective thing you can do for water heater life here.

A noisy heater is rarely an emergency, but it is a countdown. Getting ahead of it is considerably cheaper than replacing a flooded floor as well as a tank.