I completed a one system heating maintenance. I replaced 1-20x20x1 filter at air handler filter rack. I checked amp draw on the blower motor and heat strips. I checked temperature rise and confirmed zone operation. I checked the defrost cycle and charge on the outdoor unit. I checked the amp draw and capacitor for the outdoor unit. Tenant mentioned the downstairs thermostat had an issue prior. The system did not come on down stairs until they turned the fan to auto. I checked into this and tested the thermostat and system functions. At this time the thermostat is functioning correctly and system is operating with the fan in auto. I discussed system operations with the tenants and the tenants will monitor the system. I asked that if this does happen again to please take a picture of the thermostat. This could help see the issue while it is occurring.