Cleaned and checked gas boiler with 3 fan/coil units. Replaced air filters. Inspected and cleaned heat exchanger. Checked flue piping and draft. Cleaned burners, pilot, and flame sensor. Checked voltage and amperage draw of pump. Bled air from system in Attic. I found expansion tank Schrader valve leaking! I Drained and replaced Schrader valve. Refilled with nitrogen. 22psi. boiler pressure regulator: 21. Replaced air filters. Clean and check humidifier for living room system, replace pad, checked water flow and drain.