I used a little toolboard I found online (see pic), and although it worked for a few months, it appears that the 12v on the HE and Parts fan, is also connected to the HE heater on this little board, so is shorting. Although not immediately, I expect this has caused severe damage to both boards over time, which has now shown itself.
I guess you live and learn! Something I should've double checked prior to using this board!!