A pump in a HAMMER model is initially off, in anticipation of performing a pump startup transient run. However, after calculating the initial conditions, the pump is turning on.
The first thing to check is to see if there is a control associated with the pump. The easiest way to do this is to select the pump and open the Properties display. Find the Operational section and click the ellipsis button in the Controls cell.
This will open the controls dialog filtered for just the pump. If there is a control there, it may be turning the pump on based on condition. The two best options you would have would be to either delete the controls associated with the pump or to create a new Control Set that does not include the pump control. More information on creating controls and control sets can be found at this link.
If there is a simple control that you want to remain in the model, you can also make an adjustment to the Steady State/EPS solver, which governs the initial conditions calculation. In the Steady State/EPS solver calculation options, there is a property called "Use simple controls during steady state?" If you set this to False, the control will be ignore for a steady state initial conditions calculation.
If there are no controls associated with the pump, check the user notifications for any red items, such as Network Unbalanced messages. If a red user notification occurs, the results should not be trusted and the issues mentioned should be fixed before running the transient simulation. This link has details on the Network Unbalanced message and some things you can do to resolve it.
The Modeling a Pump Start-Up Transient Event in HAMMER V8i TechNote has information on modeling a pump startup simulation in HAMMER.
Pumps not following controls