Fire 3 days after closing- Insurance doesn't want to pay!

Hello Bigger Pocket family. I recently purchased a 6 unit property. Within 5 days of closing on property. My on staff maintenance worker went to fix a radiator leak in the property. He was removing a radiator valve with a hand saw, the saw made a spark, the wall paper caught fire and within 5 minutes.. the fire spread in this 120 year old building. 3 apartments were damaged $170,000. After an investigation by the fire marshalls and 3 private fire investigators. It was deemed an accident. Now, the insurance company has decided they do not want to pay the claim. The property had a vacancy stipulation on the policy that allows for the property to be vacant. 5 units were vacant, the last family had not moved out at the time of the fire. They were do out the following weekend. Im trying to see if I have a claim against the insurance agency. Any advise is greatly appreciated.