We use three forms of protection for our chillers.
(1) Temperature
(2) Differential pressure
(3) flow
However we no longer use paddle type flow switches, for some time we have been using a flow sensor which works on the principal of heat dissapation, brand name Turck. Check them out if you are interseted in getting away from conventional flow switches which we also had many failure issues with. We have been using this other type of flow switch for about 8-10 years without issue or incident.