Drupal - EntityFieldQuery display pager

I suspect the only thing you're missing is adding the return from theme('pager') to the content you're building.

This is a small example that shows teasers for all nodes in the system, with 10 per page. You would use this in a page callback function:

$query = new EntityFieldQuery();
$query->entityCondition('entity_type', 'node')
  ->pager(10);

$results = $query->execute();

$content = node_view_multiple(node_load_multiple(array_keys($results['node'])));

$build = array(
  'content' => $content,
  'pager' => array(
    '#theme' => 'pager',
    '#weight' => 10
  )
);

return $build;

More specific based on your comments:

if ($type == 21) { 
  $query = new EntityFieldQuery(); 

  $entities = $query->entityCondition('entity_type', 'node')
    ->propertyCondition('type', 'product') 
    ->fieldCondition('field_razred', 'tid', array (607,608,609,610), 'IN')
    ->pager(10) // this is the bit you're missing
    ->execute(); 

  $nodes = node_load_multiple(array_keys($entities['node'])); 
  print render(node_view_multiple($nodes, 'teaser')) . theme('pager');
}

Also been having some trouble with this - debugging statements initializePager showed that the optional $element parameter was being set to 1 rather than 0.

If there is only one pager being displayed, try setting it explicitly to 0. $query->pager(10, 0);