Can a flathead screwdriver or other metal tool be used to separate stuck plates on a plate-and-frame heat exchanger?

No, metal tools should never be used to separate plates. They can scratch or damage the sealing surfaces, which can lead to leaks or failed gaskets. If plates are stuck, a plastic mallet or plate hook should be used gently, tapping near the corners and avoiding gasket edges. If resistance continues, review the manufacturer’s recommendations before proceeding.