Upper radiator hose keep coming off

[saneesh8]

http://s1095.photobucket.com/user/sa...tml?sort=3&o=0

The upper radiator hose just came out at the radiator. Put it back and filled it with distilled water. Drove back home (8 miles). Replaced both hoses (OEM) and also the water pump (Saleri) (as PM). Reused the clamps. Old pump was in excellent shape and hose was worn. Anyway put coolant back and drove it today morning at 84F. No AC was On. After 8 miles (almost same distance), the hose came out again. Again filled with distilled water and drove it back home and came to office in the other car. Luckily both the time, as soon as the coolant started coming out, i found it stopped car. So car never got overheated. Both times, i had to put close to 1 gallon distilled water to fill it.

What can cause this?

1) Some thing blocked in the radiator
2) Bad clamp?
3) Radiator neck is bad?

Hoses, Thermostat and Water pumps are new.