As you see in the table, at 80F EWT, the pressure drop at 1.8 psi indicates about 6 gpm flow. You have about 2 PSI, so your flow through the unit is OK. That still does not mean that your flow through the loop field is OK. Again, size and length of header pipe, size of pipes in the borehole? That will tell us if one of the loops is air locked. The typical case indicating the disadvantages for pressurized flow centers! PS: ft/hd= psi x 2.3 It is just another measure unit for pressure. Also, you rely your judgement on sensors which accuracy you have not confirmed!