Gas hot water heater control unit from Honeywell, model WV8840B1110. AO Smith manufactures these for Honeywell, and OEM part # is 321166-000. This unit was installed new approximately 2 years ago in a water heater we recently replaced due to developing a tank leak.
5.0" WC Outlet, 1/2 PSI Max Inlet
This item is in excellent used condition, and was operating normally when removed from water heater with tank leak in February 2019.