John Lewis JLBIHD105 Cooker Hood- Fan Cut Out

Hi,

I bought the above mentioned cooker hood from a private seller on ebay.
I think they are made by Electrolex for JL. There is one annoying problem with it that I’m hoping someone has the answer to.
If I have the halogen lights on and have the fan set to any level above 1 i.e. 2 (mid) or 3 (high), the fan cuts out after a very short period of time, approx 10-15mins. This can’t be right surely.
If I leave the lights off there’s no problem with cut out OR if I only use lights with fan level 1 (the lowest setting).
Does the lighting circuit feed from the fan motor and thats causing the over heating? Could there be a duct block or duct kink that’s straining the motor at higher speeds?
I was thinking about installing a seperate 12v transformer just for the lights. Any ideas anyone??

Regards