Can I sue a worker for causing a fire to our home if the landlord hired him?

We were renters of a house that caught on fire when a heater technician our landlord hired was fixing it. As he closed the heater door thick black smoke was coming out of the vents and the whole roof was on fire. He did not work for a company, but was a friend of our landlords for many years. We lost pretty much everything, and what we did not lose was covered in thick black asbestos dust. Anyway, the heater technicians insurance paid us half of what we lost and said the landlord was responsible for the other half as the insurance claim was paid 50/50. I filed a claim with the landlords insurance and they denied the claim stating that in the lease we needed to carry renters insurance. Isn't it the landlords fault for not making sure that the heater technician was qualified so does that not make it part his fault, too? I am thinking of suing for the rest of the money, but don't know if the landlord will be found negligent.