Ok, so I’ve managed to get the values appearing with the following!
<?php while ( have_rows('listings_block', 28) ) : the_row(); ?>
<?php while( have_rows('listings_row', 28)): the_row(); ?>
<pre><?php the_sub_field('title'); ?></pre>
<?php endwhile; ?>
<?php endwhile; ?>
It returns the first value within the nested repeater, but it doesn’t loop through the nested rows for some reason. Any ideas as to how I could get the nested repeater looping through all of the row values?