Disassemble everything. There is a pressure seal which includes a TOP cap 0-ring that if it gets dislodged or missing, bad things will happen. It's not easily noticed, honestly, I only noticed mine when the husband accidentally dislodged his. It's not always very well seated and easy to lose. That's about all I can think of, given what you are describing. Make sure your orings on the drip tip are there too. Good luck.
Anna
Anna