What are your damages? Your septic did not fail because you went FHA. So at most if they call it in you can get another loan and your damages will be the new closing costs. You do have to understand that FHA code on the septic has nothing to do with, if you have to replace the drainfield or tank etc. Even if a home inspecton said that your system was great, and breaks 5 months later, you can not do anything unless you can prove it that it was broken before the inspection. I feel sorry for your problems, but probably you had a copy of the appraisal before the closing and at that time you should of seen the appraiser's mistake.