Hello all, I am trying to wrap my head around a Goodman furnace issue. Natural gas, upflow configuration. It turned really cold here yesterday and it was enough for a lurking problem to rear its head. I noticed that the furnace was running, but not producing heat. I popped the access cover off to inspect the burners and inducer. Furnace fired right up. I thought it was a fluke so I put the access panel back in place and the flames went out. Now, as long as the access panel is off the unit it fires and heats normally. I am thinking there is a problem with the inducer, but I am stumped as to why the furnace operates normally with the panel open, but shuts the gas off as soon as I seal up the compartment with the panel. Any ideas?

Just out of curiosity guys, we have a monster sized Thatcher 110k BTU Gas heater in this 70 year old house. I normally set the thermostat at 74 and leave it like that during the winter but on super cold and especially windy days, how high should I set it so as not to put too much strain on the heating system please?