On arrival found system set on e heat and custmer informed that pipes were frozen .i then went to unit and checked system operation,found system was locked on fp1 but no Ice on pipe .checked pump which was pulling 0.9 amps,also checked system refrigerant pressures which was normal 80psi low and 275 high which corresponds to entering water temp of 34 degrees .also checked brine level in the loop which good 0.7 . I then called water furnace and advised me to replace fp1 sensor .i then reset the faults.unit operating normal at this time Need to order fp1 sensor and come back to install it