TronXY XY2Pro Dead Fan

I have Tronxy XY2 Pro, that has worked flawlessly for about 6 months, but the fan on the hot end (the one for the heat break) has died. So I thought no problem, I'll grab a replacement fan.
So 3 fans later from Amazon I've decided I'm missing something. Using a Multi-meter, there appears to be a permanent 24v supply to the fan connector, but none of the fans are turning.
The original fan was definitely knacker, it was stiff to turn. The new fans are brand new free turning etc. but are not starting.
Anybody any thoughts?

It's quite common for these cheaper printers to have the fan terminals reversed. Pop the crimps for the fan's plug out, reverse them and see if that works.

Double checking with a test meter again, you are right, they are reversed. Swapped the wires in an extension lead (fan leads are too short for printer anyway), but now when I power on I only get 21v and fan still doesn't turn. At first I thought it was resistance in the extension, but even if I measure it at the break out board on the gantry, it is still 21v, Also voltage seems to be constant at the pins, I thought it only came on when the hotend was hot. Previously voltaage was a constant 24v no matter waht the hot end temp, now it's 21v no matter what, but I've not touched anything further back than the breakout board.

Just measured voltage with a fan attached. Voltage drops to 10v. I'm guessing that isn't normal.Swapping the connectors for the hotend fan, and the part cooling fan (pins are also reversed), the new fans (with modified extension) work in the parts cooling fan position.

I've heard of something similar with another Tron. Incorrect pins on fans is pretty common, but usually switching them around is the simple fix. I wonder if the Tron boards are missing some form of protection, and the reversed fan is damaging them.