Taxonomy Hidden List Powershell (SharePoint 2010)

I have a n issue where the taxonomy hidden list is not being updated even though I have run the "Taxonomy Update Scheduler" from central 
admin. In any case I have powershell to attempt to get this list updated
 but the powershell also has no results. Powershell below:
$site = Get-SPSite http://test-sample-site.co.uk
[Microsoft.SharePoint.Taxonomy.TaxonomySession]::SyncHiddenList($site)
$site.dispose()

Any assistance on this would be great.

Thanks