check engine light

I have a 1997 Accord 4 cyl Vtec engine, with 80K miles. Last week while my wife was driving to work she noticed that the "check engine" light came on. I met her at work later that day and drove the car home. On the way I noticed that the temp gauge went "hot." The following day I checked the coolant and found that it was low. I topped it off with water and took the car to the Honda dealer. They checked the module and said that the car had reached a temp of 380 degs. I told them to refill the coolant. When I picked up the car the check engine light was still on and they said that it could not be turned off because of the overheating and that although they couldn't find any leaks it might be a blown head gasket. Now several days later the coolanr level is still high in the radiator. My question is , if there were a leak wouldn't it have shown up by now? And, wht must the check engine stay on as the dealer said?
thanks,
Mike