Preventive maintenance: Doesn't always work

[Ford Falcon XR6]

Hey everyone i had a little bit of bad luck on the way home from work the other day my car ended up blowing the hose from the heater bypass pipe to the heater tap pics below. The hose must have blown on my way to work without my knowing then when i went to drive home the car got very hot very quickly. I replaced all these hoses 12 months ago with gates hoses as i like doing preventive maintenance.
Long story short i took the car back to work and replaced the hose and pressure tested the cooling system which was all good. But now my car doesn't seem to get any pressure in the cooling system even after a half hour drive to work (with some spirted driving) Any ideas why the could be ?? There is not noticeable coolant usage but i have done a whole lot of driving since this happend. Thanks in advance Lorenz.