I came at this from a different direction, years ago I fitted a water flow activated buzzer in the raw water line after the pump. It will sound on start till water flows, or during running if raw water flow is interupted[blocked filter, impellor fail etc] The only time it has gone off for real was when I failed to open the sea cock OOPS. Simple mechanical flow switch has stood the test of time ,plus I dont have to check a gauge. Geoff