To avoid confusion over debits and credits, avoid thinking of them in the way that they are used in everyday language, which often refers to a credit as increasing an account and a debit as decreasing an account. For example, if our bank credits our checking account, money is added to it and the balance increases.
One way to reduce the frequency of this occurrence is to maintain an air pocket at the top of the water heater tank. This air pocket will form in the tank by design - however, it will be reduced over time by the everyday use of your water heater. To replenish this air pocket: Turn off the water heater.
Traditional hot water circulating systems use a hot water circulating pump to pump hot water from the water heater, through the hot water piping, and on back to the water heater through an additional length of pipe that runs from the furthest fixture back to the water heater. This provides you with instant hot water.