UIRefreshControl on UICollectionView only works if the collection fills the height of the container

Try this:

self.collectionView.alwaysBounceVertical = YES;

Complete code for a UIRefreshControl

UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init];
refreshControl.tintColor = [UIColor grayColor];
[refreshControl addTarget:self action:@selector(refershControlAction) forControlEvents:UIControlEventValueChanged];
[self.collectionView addSubview:refreshControl];
self.collectionView.alwaysBounceVertical = YES;

Attributes/Scroll View/Bounce Vertically in Storyboard/Xib

Larry's answer in swift:

    let refreshControl = UIRefreshControl()
    refreshControl.tintColor = UIColor.blueColor()
    refreshControl.addTarget(self, action: "refresh", forControlEvents: .ValueChanged)
    collectionView.addSubview(refreshControl)
    collectionView.alwaysBounceVertical = true

Swift 3:

    let refreshControl = UIRefreshControl()
    refreshControl.tintColor = .blue
    refreshControl.addTarget(self, action: #selector(refresh), for: .valueChanged)
    collectionView.addSubview(refreshControl)
    collectionView.alwaysBounceVertical = true