Pumps will lose their prime if run dry or previously winterized. You can disconnect the hose from the intake side and attach another piece of hose with a funnel and pour water into it while some one switches on the pump. Once it starts sucking water, turn off pump and reconnect input hose and try the pump. Sometimes you may have to actually blow water into the pump to get it started.
This is the strangest life I've ever known - J. Morrison
2015 Airstream International Serenity 27FB with ProPride
2011 Ford F150 Lariat Ecoboost V6 Turbo Gasser