Performed pm on oil boiler Brushed and vacuumed flue pipe and heat exchanger Replaced oil filter, nozzle, and strainer Checked all electrical connections and safeties Performed combustion and smoke tests While performing the maintenance we found 2 hi-vent that have corrosion on them showing they have leaked in the past and are no longer functioning properly. Found the oil shut off valve at the burner is not closing fully and is still leaking oil by to the strainer even when the valve is fully seated. Tested the autofeed and found it is not letting water through. Recommend replacing the oil shut off valve, 2 hi-vents, and autofeed and backflow combo.