I had a plugged line in my drain for the furnace it would cycle but would not fire up .I unclogged the blockage with a shop vas but it seems the furnace is in lock out mode how do you reset you furnace so it will cycle properly and have heat.The furnace firsts cycles when you turn up the thermastat but looking through the glass peep hole the furnace trys to start up but no success ,cycles through a couple of times and then shuts down or blows cold air.