I have a heil furnace 9mpd, model h9mpd075f12b1. I was/am getting some heat but not up to the temp setting on the thermostat. I have a code of 1 flash followed by 6 flashes. I put new batteries in the thermostat and opened the furnace to see the code. Soon after the furnace kicked on and seems to be operating properly. Do I have a furnace problem or was the battery replacement the fix? Thanks.

I don't think it's stat. That flash code is soft lockout, flame failure. Try cleaning the flame sensor.