Thermostat is not working downstairs. We have a dual zone system on an open floor plan 2-storey house. Upstairs thermostat is working fine but suddenly no heat coming out of downstairs vents. Thermostat downstairs is an old heating-cooling Janitrol CHT18-60. When I turn the switch to fan, cold air blows out, but when I put it on auto, fan stops. What should I do? This unit was working fine yesterday. Today we are freezing downstairs. I can hear a click when I turn up the thermostat and something humming but no air. Help! System is gas pump( I think). Thanks!