Customer called because of water leak on boiler. Service technician found boiler and piping dry on arrival. There are traces of previous leakage leading to the auto vent and some water at the vent screw. Shut vent screw on auto vent and customer to watch for leak. Ran boiler and found system pressure went from 12 to 20 psi. Checked expansion tanks and the lower one is bad and should be replaced. Pressure may be swinging enough to make auto vent leak, but auto vent should be replaced as well. Customer complained of low flow of hot water. Tankless hot water coil in boiler appears to be clogged, recommend replacing the coil. Will get parts info and update ticket with repair estimate. Customer very happy with service and will highly recommend Advanced Heating & Cooling.