If that doesn't work, perhaps disconnect the switched live feed and see what happens? Have you checked the wiring with a meter to confirm the switched live is exactly that. Also is there a jumper in the fan that needs removing for timed operation?
@wvm started
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If that doesn't work, perhaps disconnect the switched live feed and see what happens? Have you checked the wiring with a meter to confirm the switched live is exactly that.
Also is there a jumper in the fan that needs removing for timed operation?