Check for > 0 in texbox

Greetings again,

I am trying to check the value of a textbox, which has data imported from a datagrid, and am needing to check and see if the number imported to the textbox is greater than 0.

I have tried checking for just 0 but it doesn't appear to find it.

If CDbl(TextBoxTier1.Text) > 0 Then RadioButtonTier1.Checked = True

I have also tried

If TextBoxTier1.Text = "0" Then RadioButtonTier1.Checked = False

Thanks for any help.