There is a refill process in that you turn on the heater and unscrew the bleed hose while the engine is running, while topping up the coolant. A warning light will also trigger if the coolant is too high. If a head gasket goes it is quite violent with smoke, coolant blowing out, misfires. No way that has happened there, I think it has not been refilled properly and there is still air in the system but that is all.