1) Push up on valve from the bottom until the top and the o-ring is accessible.
2) Remove and do not lose the o-ring.

3) Remove the valve and spring assembly through the bottom.
4) Slide the spring back onto the valve from the top of the valve to the bottom end.
5) Insert assembly from bottom and push up from the bottom on the valve and put the o-ring back on from the top side.
6) Lower the valve, the o-ring will now hold the assembly in place and it should function normally.
I hope I'm the only one this happens to but if not hopefully this will save you the expense/PITA of getting new parts, etc.
Have a great holiday season!
Scott
Cheers!
Scott