Further reading allowed me to gather the following advice. Firstly, my sewing machine manual suggests to replace a needle 'regularly, especially if it is showing signs of wear and causing problems'. Problems are skipped stitches , upper thread breaks, noisy machine or the needle breaks.
Shea Henderson in School of Sewing gives the following advice, replace needle each time you clean your machine, after every large project or after eight hours of sewing.
Good advice but I was thinking it would be lovely if my machine had a warning light that just lit up when I needed to replace the needle , like my car does when something is not working right.
A sharp needle gives the best sewing results. so if you are experiencing stitch problems or cannot remember the last time you replaced the needle do it today.
If this is the first time you will be changing a needle please refer to your sewing machine manual for instructions.