Help!! furnace is not working properly, house is VERY cold?

we bought our house about 4 years ago and the furnace has worked fine, but the past few days it hasnt, our thermostat is set at 70 the house is 62 and im in new england so its a little chilly still so we need the furnace for a few more weeks.the maker is "the new yorker steel boiler" model# s 580-1. serious answers please