Symfony 2 - separate form logic, show form errors after redirect

I want to separate form validation logic:

public function contactAction()
{
    $form = $this->createForm(new ContactType());

    $request = $this->get('request');
    if ($request->isMethod('POST')) {
        $form->submit($request);
        if ($form->isValid()) {
            $mailer = $this->get('mailer');
            // .. setup a message and send it

            return $this->redirect($this->generateUrl('_demo'));
        }
    }

    return array('form' => $form->createView());
}

I want to translate into 2 separate actions:

public function contactAction()
{
    $form = $this->createForm(new ContactType());
    return array('form' => $form->createView());
}

public function contactSendAction()
{
    $form = $this->createForm(new ContactType());
    $request = $this->get('request');
    if ($request->isMethod('POST')) {
        $form->submit($request);
        if ($form->isValid()) {
            $mailer = $this->get('mailer');
            // .. setup a message and send it using 

            return $this->redirect($this->generateUrl('_demo'));
        }
    }
    // errors found - go back
    return $this->redirect($this->generateUrl('contact'));
}

The problem is that when errors exist in the form - after form validation and redirect the do NOT showed in the contactAction. (probably they already will be forgotten after redirection - errors context will be lost)