We are new owners and trying to learn about the home's irrigation system. It is an underground two zone system that has a 1.5 HP pump irrigating lake water to the yard. Some days it works perfectly. Other days...seems to be on windy days the system turns on and then gradually loses power until there is no water coming out of the sprinkler heads. If I shut it off and wait a minute or two it will repeat the same pattern of events. the pump looks to be about 20 years old...same as the house. WE have cleaned the sprinkler heads so that is not the problem.

Any ideas on how to fix this problem?