from the OP:
"the pump was continuously running and the water was spitting between water and air, but mainly on the hot water side".
If its not the filter, i was offering another possibility to check for an 'air bubble' on the HW side . It doesn't cost anything except a little time, so i figured , why not try it ?
I had what i think was the same thing happen to me. After i did this procedure, it seemed to clear things up.
I was thinking a spitting of air and water from the HW side might be an air bubble in the WH .
I didn't know what to do and just took a stab at doing this , that's why i tried it . Who knows if it was the the correct thing to do or not but i now have HW and no spitting. :h