2006 Vauxhall Corsa overheating engine

The temperature warning light came on in my car (it doesn't have a temp gauge fitted) when I check the coolant reservoir was empty I've been topping it up every day - (the light didn't come on again after that for about a week) I booked it into the garage to be checked out. A few days before it was due to go in the car the warning light came back on the the car lost poor. I called the AA who discovered the connection to the hose on top of the water pump had broke and coolant was leaking from there.

The connection was replaced but when driving home the warning light came back on after driving about 5 miles. I called and took it back in the following morning they have since checked the water pump, the thermostat, hoses etc & did a dye check on the cyclinder head gasket which were all fine but the engine is still overheating and the warning light coming on intermittently anyone got any ideas whats wrong?