How does one activate a pivot table refresh from a userform ?

I tried to use this code in the command button without success:

ActiveSheet.PivotTables("StoichiometrySt1").Refres hTable

I think the code doesnt work because the userform is activated in another
sheet

Also, is there a way to suppress the warning dialog asking if you want to
replace the cells when you refresh the pivot table

Can anyone help with either of these questions?