You get a call: sump pump running nonstop, basement not flooding yet but the homeowner is nervous. You get there, check the pit — water isn't rising. You pull the pump, find a small rock lodged in the float housing. Clear it out, float moves free. Plug it back in.
Pump cycles once, then stays on. Won't shut off. You checked the discharge line — clear. Check valve — working. Float — moving free.
What's your next move?
What's your diagnosis? Drop your best guess in the comments.