When I first turn on the heat, the gas furnace lights up appropriately, it heats and then the fan turns on and blows the warm air. After about 1-2 hours, the air is still blowing but it is now cold air. In order to get it hot again I turn the breaker to the furnace on and off and the cycle starts over again. Is the board the issue? Is the furnace overheating? It is a 1995 York furnace.