Performed annual tune-up on a Buderus propane boiler. Cleaned the burner, heat exchanger, igniter, and flame sensor. Inspected safety controls, venting, and overall hydronic system function. Replace failed expansion tank, leaking relief valve and piped relief valve to within 6 inches of the floor. Bubble-tested the gas line and checked carbon monoxide levels—no leaks detected. Verified proper operation; the system is functioning correctly at this time.