Why is my jet ski overheating?

My Kawasaki deluxe 250 starts overheating after running for only a few minutes (by 'overheating' i mean beeping and the warning indicates "heat" and I've also seen "F1"). The innercooler is extremely hot, but nothing else is. It was just serviced and I assume it was flushed so nothing would be clogging the intake. What else should I check or have tested.