Check the gas supply valve and open the valve if the Lennox furnace has power but the pilot light is not lit and the furnace is not operating. Ensure that the power switch is set to “On,” if the gas supply is operational.
Turn up the thermostat several degrees if the furnace is on and the pilot light is lit but the furnace is not running. Move the switch to “On” or “Heat” instead of “Auto” and allow several minutes for the furnace to start and begin to heat the home.
Switch the power to “Off” and wait for the furnace to cool if the furnace is not heating appropriately. Remove the access door and slide the filter out of the housing. Clean or replace the filter, put the filter back into the unit and shut the access door.
Open all the registers in the house, if the home is not heating evenly or is running loudly because shutting one or more registers can create a pressure imbalance. Keep items off and away from the registers for better air flow.
Check the blower wheel, if the furnace is noisy when operating. Clean with a long-handled brush to remove debris and dust.
Disconnect power to the furnace if the pilot light is not lit and lower the thermostat to the lowest setting. Rotate the gas valve control to “Off” and wait five minutes. Sniff for gas after five minutes and leave immediately if you smell gas. Call your gas company. Turn the control to “On” if you can't detect a gas smell and shut the access door. Turn on power to the furnace and turn the thermostat back up.