Using a pivot table as the source data for a chart

I have several charts that are using a pivot table as their source data. To do this, I just clicked on a cell in the pivot table and then clicked on the chart wizard. The charts come out just fine. My problem comes along when new data is added to a pivot table. The charts do not update themselves with the new data. Actually some of the charts do and some don't I can't figure out what the difference between them is.

Basically I would like to know how to make a chart that will always update itself when it source data (a pivot table) is updated.

Thanks