Right, my brain is hurting now because I can’t get my head around this….
My old bathroom fan had intermittent issues, when turning it on (separate switch to the lights) it would spin for a couple of seconds then stop. I’ve fitted a new fan, and I still have the same issue? I’ve taken the fused switch apart and everything seems in order, also fitted new fuses?

Anyone know what might be going on?

Are the switch contacts in the fused connection unit a bit duff? I’ve seen switches which are knackered and momentarily make contact when you turn them into the on position but keep the contacts closed. Easiest way to check is temporarily wire the fan onto the supply side of the FCU bypassing the switch. good luck!

Is it on a timer ?

I’ve given the contacts a clean where the fuse sits, the fan has a timer on it which I’ve twiddled either way but to no avail, I think there may be some voltage drop transistor somewhere?

if the brand new fan is showing the same problems as the old one, i reckon it’s the fcu. Wiring up the fan directly to the supply side (obviously turn the power off first) will confirm that.

I agree with spectraken – its a fault on a switch

There may be a separate humidistat hiding somewhere or if it’s a 12v fan the transformer may have other controls ?

yeah , did you fit a new tranny as well if its a 12v ?. think the guys above are right, dodgy rocker on the switch. or possibly a slightly loose main in the connector at the light, assuming the feed isnt direct to the switch?

No haven’t fitted a tranny yet, I haven’t located it either! Is there a usual place where these are? There isn’t anything near the switch or fan?

I’ll bet the switched live on the fan switch is loose/corroded. Try a new switch .