For salary/wage earners only:
1) Request a summary of earning for the year you are looking at,
2) Quick calculation by using the IRD wedsite calculator,
3) If the result is a refund then request a Personal tax summary,
4) Once you have received your personal Tax summary, give IRD a ring and they should be able to sort out the refund for you on the phone.
Do not request a "personal tax summary" if you don't need file a return, by requesting a personal tax summary , IRD will expect you file a return.