American standard high efficiency variable speed multi-stage system is running in very good condition after today's service. Install replacement aprilaire 213 air filter media supplied by homeowner, replace #35 humidifier pad supplied by service truck stock, test run humidifier and set to 35%, run test two stage heating, plenum temperature 136 on high stage, resurface flame sensor and inspect ignition system, disassembled drain trap for heavy duty cleaning. Light duster cleaning on the entire system Excessive corrosion leaking from thermostat batteries. Clean thermostat contacts, replace batteries, test run