Cooling problem

My friend drives a 1993 jeep grand cherokee, apprx. 175k miles. He and his dad just installed a new radiator with new hoses but the coolant is not cycling through the engine. It backs up in the upper hose, has broken through the thermostat seal and is leaking onto the engine. Is there an internal problem or do the hoses need to be checked again? Any thoughts? Thank you.