Web Forms :: Using ValidatorValidate With ValidationSummary

I'm trying to get a textbox to validate onblur. I have the following code:

myPage.aspx:
<asp:TextBox ID="txt1" runat="server" /> <asp:Button ID="btn1" runat="server" Text="Submit" OnClick="SubmitForm"/>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="No text" ControlToValidate="txt1" Display="None">
<asp:ValidationSummary ID="ValidationSummary1" runat="server" />
myPage.aspx.cs:
protected void Page_Load(object sender, EventArgs e)
{
txt1.Attributes.Add("onblur", string.Format("CheckForValue('{0}');", RequiredFieldValidator1.ClientID));
}
protected void SubmitForm(object sender, EventArgs e)
{
if (Page.IsValid)
{
// process ...
}
}
myPage.js:
function CheckForValue(sender) {
var control = document.getElementById(sender);
ValidatorValidate(control);
}

The validation control will validate if I set the Display to Dynamic or Static, but it won't display the error text in the ValidationSummary when the onBlur event is fired (its fine if the form is submitted using the button). Does anyone know if this is a restriction of using the ValidatorValidate function or am I doing something wrong?