Cleaned and serviced on gas boiler, pulled burners and cleaned, vacuumed burners and around boiler, tested thermocouple which tested normal, gas pressures normal, tested all three zones which all opened and closed, inspected water components, expansion tank good boiler pressure at 15, relief valve is new, do recommend changing air vent due to corrosion left customer estimate to replace, all supply and returns got hot, combustion test performed which system looks normal,