Greeted tenant and proceeded to perform a PTU on a gas fired furnace. Opened up the cabinet, checked and inspected the following: electrical wiring with connections, inducer fan assembly, pressure switches, hoses, rollout, flame sensor, spill switch, gas valve, etc. etc. Restored power to the furnace and turned it on. I observed the furnace light off, run, cycle and reach temperature. All is good at this time. The furnace could use several preventative services. 2nd service requested; unable to perform the service, due to the fact that the owner was not present to open the door which is under lock and key.