Your furnace might show numerous signs to get it repaired or replaced. These reasons can be varied and you should never ignore these to prevent further damage to the furnace. Different types of smells coming from the furnace Longer heating and cooling cycles Furnace shutting off and on repeatedly Loud noises made by the furnace Furnace not cooling An issue with the pilot light Faulty parts These are the most prominent issues that can make your furnace need repairs. But you should never ignore an abnormality and always call a professional as soon as you detect an unusual issue with the furnace.