Cassette toilets

Do you have SOG fitted? If so is the valve/blade not fully shut so the fan is running?

....but a SOG fan only runs when the blade is open....

on closing the blade, the fan should stop...

also, rhe OP mentions being on EHU, the sog should run off 12v and therefore work whether hooked up or not.

it could be that the SOG has been wired incorrectly and is working in reverse....ie fan running when blade is closed....?? 

Thank you all for your support I do have a sog fitted I will look at the system again this week end . Pete.