I arrived and met with Bill. He showed me three unit heaters that were not functioning. The unit heater on the south wall was diagnosed with a high temperature safety switch that was tripped. This unit is very close to the ceiling and after inspection I could not determine why the switch tripped. The heater was operated for an extended amount of time while the temps were checked to confirm that it is functioning properly. It is a possibility that being so close to the roof and the below freezing temps last year that the thermostat kept the unit operating and the temp at the ceiling was elevated while the temp at the thermostat was still asking the equipment to operate. The heater in the S.W. corner was diagnosed with a failed ignition control board. This was sourced, replaced and heating functions were checked after the repair. This unit is back in service. The heater facing dock door #4 had a pinched thermostat wire that was routed into a grounded screw