Thumper problems

Hi,

I recently bought myself a thumper. I have a GF with the copper dome, and extended it with a thumper.

I put some low wines in the thumper (about 1/3 of the thumper) , but when I start distilling the liquid in the thumper starts boiling and it fills with water, so before any liquid comes through the condenser, the thumper overflows and the low wines in the thumper are diluted.

What am I doing wrong here 🙄?