C# - Changing AppSetting Does Not Have Effect On Application?

In one of the application i am developing on ASP.Net. In this application we have been using lots of AppSettings. In the initial development we used ConfigurationManager.AppSettings[""]. but as development progressed we created a utility class in which we would define a static property for each AppSettings. Then issues started to come. Now when application is deployed on testing server and we change any settings on AppSettings it does not have any effect unless we restart the IIS. here is the following code snippet i am using to create static property of AppSettings.

public static class AppSettingsUtil
{
public static string Log4Net
{
get
{
return ConfigurationManager.AppSettings["Log4Net"];
}
}
}