Is it losing prime? What brand of pump is it? Is it just a circulator or is it like a shallow well or jet pump? Do you have a backflow preventer on it or a swingcheck valve. If it is just making growling noises it could need lubrication, but if it is having problems priming itself or retaining prime you could have a low water supply, or the pickup screen could be sitting in mud or silt. Usually if the pump motor runs in the first place the problem is not with the pump, but with the surrounding valves, water supply, piping and so on.