Completed annual maintenance on one gas boiler, pulled burners and cleaned, vacuumed around boiler, tested water components and noticed expansion tank had failed due to boiler at 28 psi and tank rock hard, also noticed air vent very corroded, and while running system gas valve making a loud buzzing noise, replaced expansion tank, air vent and gas valve, purged 3 zones and a indirect water heater zone, took combustion test which was normal, gas pressure on new gas valve normal, tested all zones all came back hot on supply and return side, system operational and working. Please mail invoice to customer.