With even a handful of miners it is essential to carry spares. It is not worth returning a miner for faulty fan or PSU, because they are so cheap and you'll lose more in downtime, plus the risk of damage in the post.
I have approx. 200 miners total across 5 small farms. I reckon I get through at least 50 fans and 5 PSU's each year, and 1 or 2 control boards.
I'd recommend to keep as spares:
1 PSU for each 20 miners (with min 1 in stock at all times)
1 control board per 50 miners (with min 1 in stock at all times)
1 fan per 2 miners
I buy all my spares from ZeusBTC (import from China).
Yeah they toss fans like mad
so its good to have them.
once you pull a dead fan and you are certain it is dead.
cut the power cable from it as close to the fan as possible and save the four wires attach to the connectors.
you wont mistakenly try the dead fan again. and once in a blue moon you may need the four wires and the white connector