Customer has 15 y/o Tempstar system that operates for whole house. Furnace located in crawlspace. Performed routine maintenance inspection of furnace only. No noise detected. During inspection gas valve failed causing no heat. Cleaned flame sensor. Cleared pressure switch tubing. Heat exchanger is rusted. Poor combustion. Rusted burners. Blower wheel cleaning needed. Damaged return duct. No form of water protection. Recommend iWave-R Air ionizer to purify air and prevent duct buildup. Based on our findings today, it might be time to think about getting a brand new system.