Welcome to the forum. Tell us a little more about the make and model, as each has its tricks. It sounds possibly (and I'm the least technically competent hot tub person around here) it could be an air lock. If this was my tub, I would take the filters out and put the fill hose directly into the the vacant holes. My tub also has a relief valve that I could open while doing this and that would force air out of the lines. Did you fill the tub this way, or just buy dropping the hose inside the main part of the tub?
