I have a furnace approx. 20 years old, one stage. When the outside temp gets extremely cold (single digits), the furnace acts up. The pattern is usually around 4 in the morning, the furnace stops producing heat and blows cold air. But it still attempts to cycle, so the thermostat seems to be working as it should. When I turn it off and let it sit for a few hours, it begins working normally again. I assume this is an overheating issue, because when it gets that cold the furnace is cycling on and off almost continually. Is this something that can be repaired, or am I better off just replacing the furnace. And if the latter, would a 2-stage be more advantageous? My home is a 2-level townhouse approx 45 years old. The ductwork has been amended over the years and the furnace location is extremely tight. I have owned the home less than 2 years, so don't know the service history, but I had it serviced last year and was told it was in decent shape. As an FYI, I have noticed the last two summers that the A/C has a similar pattern, though very infrequent - maybe a couple times in a season. Thanks for any advice.