Carefully inspect the head for cracks and signs of coolant intrusion. If cracks or visible damage are found, replace the head. It is recommended to check for microcracks in a car service using Magnaflux methods (magnetic flaw detection technique for cast iron heads), or Zyglo (fluorescent spray technique for aluminum alloy heads).
Check for obvious mechanical damage to the head (curvature of the studs, breaking off of the material due to an accidental drop of the head, etc.). In case of serious damage, replace the head.