1998 Honda Civic Cracked cylinder head

A year ago I had my cyclinder head, thermometer and radiator replaced in my Honda Civic after it had several incidents with overheating. I've only driven it six months out of the last year (I was in Iraq) and only put 7,000 miles on it since the head was replaced. Severals days ago it began overheating again. I pulled over immediatley and found that the lower hose that connects the radiator to the engine had come loose. It appeared that enough pressure had built up that the hose had blown off, there was coolant everywhere. I replaced the hose and took the car to the Honda dealer that had replaced the cylinder head. I was told that the new one is bad too and that I will have to replace it. What are the odds that 2 cylinders head would fail in such a short period of time? What could cause pressure to build up in the engine and force the hose off? Am I off the mark in thinking that perhaps the replacement was not properly installed?