[Steve Tinker]

It certainly sounds like you have dislodged a coolant pipe, though I must say that on all the writeups I have read re removing the AOS, I don't remember having to remove or even move any coolant lines....

As with all things after the fact, go back to basics and check all equipment you removed or disturbed when replacing the AOS.
Of course, you could just have had bad luck and split the coolant bottle while pushing and tugging pipes in that general area.

1)Look for coolant in the rear trunk - cracked coolant bottle.
2) Check coolant cap is on correctly and not leaking (Part No should end on 04).
3)Just to ensure you haven't an air lock, raise the D ring under the plastic cover where the oil filler / coolant filler is located. You can run the engine for a few days (several heat cylces) with it opened, all the time checking coolant level & topping up as required.