Rumbling, popping or knocking water heater

The popping or rumbling you hear from a storage tank is water flashing to steam under a layer of sediment on the tank bottom: the burner or element heats the sediment, moisture trapped underneath boils, and the steam bubble pops up through the layer. It is the sound of the tank's heat transfer degrading, and it is most noticeable on gas tanks with high-input burners and on electric tanks where sediment settles around the lower element.

Occasional popping after a long idle is common; steady rumbling during every firing cycle is the tank telling you the bottom needs attention. Metro Vancouver's soft water slows sediment formation, but tanks still collect it over years, and homes with older galvanized supply pipes can collect rust and debris.

Sediment is not just noise: it insulates the tank steel from the water, so the bottom runs hotter than designed, which accelerates corrosion and can eventually overheat the tank bottom itself. On electric tanks, a sediment-encrusted lower element runs hot and fails early. The manufacturer maintenance schedules that call for periodic draining exist to prevent exactly this.

A rumbling tank that has never been flushed is a candidate for the maintenance visit rather than the scrap pile: drain and flush the sediment, inspect the anode, and check the bottom for hot spots, which a technician does with the tank cold and isolated.

Not every knock is sediment. Water hammer is a plumbing noise that happens when valves close fast, usually at the fixture rather than the heater. A whistling or hissing tank can be a flow restriction or a valve issue. If the tank is also leaking or the water is rusty, sediment is no longer the main story: the tank bottom may be failing, and the visit decides between a flush and a replacement.