spring in the upper hose? Hopefully, the lower has one as well as it is the one that can get sucked shut...the upper has pressure on it so it cannot.
You should be able to hold the upper hose and see if water begins to circulate shortly after it reaches the stat temp. Hose will suddenly increase in temp. An infrared temp gun will also show the jump
As far as the air, run it a couple of times, let it cool and see if it is full...or nearly full...when you remove the cap. usually, opening the heater and letting water circulate thru it will help push trapped air out, I have found.