Overheating

Hi i have a 2006 ford bantam rocam. I had to
replace thermostat housing and heater control
valve. After i had replaced both the car would run
fine on the highway for 80 kms to my place of
work. Once i arrived and the car was stationary the
needle would rise rapidly into the red. Eventually i
pulled everything off again flushed out the system
put a new water bottle in and bled the system to
make sure no air was trapped inside somewhere.
Still to no avail. Then i opened the new housing a
discovered that the thermostat was not opening
(tested with boiling water ). So i removed it
temporarily and put everything back together so
that i can get to work and buy a new thermostat to
install. Driving without the thermostat was fine
until i once again stopped at work and once again
the needle rised rapidly into the red. Fan is working
100% . When i opened the bonnet i discovered the
bleeder pipe was cold. So i slightly opened the
water bottle to allow air to pass and then it allowed
the breather pipe to pass the coolant back into the
bottle. I tested the waterpump and it is working
fine. But without the thermostat it shouldnt
overheat ? . Also is the water bottle cap supposed
to allow air in when needed ?
Im scratching my head at the moment and am
unsure of what the problem could be . Can anyone
please help ?

Regards