The pump motor is failing. It is drawing too much current and overheating causing the breaker to trip (either electrically or internally). You will require at minimum a new pump motor, and often a new replacement pump altogether is easier though a little more money. Since you should be shopping for a new pump you should strongly consider a variable speed pump. It will pay for itself over and over again in electrical savings. Here are some of the most popular models of variable speed pump and some more detailed info on how and why they save you money: Variable Speed Pool Pump Reviews