Arrived on site to complete heat season maintenance. Inspected systems in heat test mode and verified proper operations and documented all findings. Found unit 2 to not be firing. Unit was locked out on no flame code. Tested system and found gas regulator not passing gas flow. Open and and closed regulator to free debris. Unit fired up and is operational. Getting the Regulator replaced will stop this from happening again. Also found same u it to have chattering contactor making noise. Needs replacement as well. Waiting quote for replacement. Maintenance complete.