With an FHA loan, the pool should be in working order. Problem is that it is up to the appraiser to ensure the lender (your lender) that the pool is working. Really all that means is that the water is clean and clear. It would be nice if they at least would run the filtration system, but if the water looks good, they will most likely call it good. Keep in mind that it won't take long for a non functioning pool's water to turn green.
The only way to have protected you from any unforeseen repairs, would have been to have the pool inspected at your cost by a professional home inspector.
Hopefully as the others have said, you did have that done. An inspector can not be held liable, but refer to that report and see if there was an indication of a problem. You had a due duligence period for that investigation and if anything negative was found, your agent should have guided you to request that the seller make the repairs. Or at that time you have an opportunity to back out of the contract. Bank owned home sellers (the banks themselves) usually will not make any repairs unless they are required by your lender.
That in turn, takes us back to the appraiser. The likelyhood of the pool not working when that appraiser came through is slim.
At this point, I would make sure that you are talking to a reputable pool repair company before contacting your agent for assistance. Take those steps first before bringing in an attorney. Your only true recourse there will be if your agent did something wrong.
If you need any further assistance, I'd be happy to talk with you more about it.