Why does a hot water tank gurgle when you turn off the hot water?

Answer 1

Older water heaters have been in the house for a while and usually build up sediment in the bottom of the tank. This can be calcium deposits that have broken off and sand that came in the house with the water. In any case, once you have sediment in the tank the water heater won't work anywhere NEAR as efficiently as when it was new. Water heaters turn on when cold water comes into the tank. Cold water comes into the tank when you use some of the HOT water that is in the tank. When a gas water heater turns on the flame heats the bottom of the tank. If sediment is on the bottom, the water does not move quickly out of the way, and instead stays trapped in the sediment until the small amount of trapped water reaches boiling point. Then it explodes into steam and moves out of the way, allowing more water to slide back in to the small area among the sediment. The process repeats and makes a gurgling noise that is really little more than a warning that you are about to buy a new water heater. You can greatly increase the life expectancy of a water heater by periodically draining a little water from the water heater using the water valve that is near the bottom of the tank. You only need to drain a few gallons, but do it regularly, at least every month or two.