property closed 27 nov 2017 $5000 in escrow for boiler seller unable to fix but wants to release only $1000 which cannot fix it what’s my option

I closed on a property on 27 nov 2017 but the realtor at the time of the final was unable to put on the boiler but said it was working so I advised my lawyer to put some funds in escrow until we are able to confirm at closing the seller said it had to be fixed and give him 2 days which resulted in 3 weeks and 4 different plumbers and still unable to fix it and they refuse to release the escrow after some back and forth it was suggested $2500 to get it fixed I agree and now they are saying $1000 please advise