Most ovens have the fan accessible fmr the back under a removeable panel.
Obtain correct new fan fo rthe make and model of oven (espares, for instance)
Switch oven off at the main
Remove oven, making notes on a bit of paper what screws and bits go where
remove back panel, making notes on a bit of paper what screws and bits go where
Probably - inside the oven remove the shelves, making notes on a bit of paper what screws and bits go where then remove the back of the oven cavity, making notes on a bit of paper what screws and bits go where.
Remove the fan blade
from the back of the oven, disconnect and remove the motor, making notes on a bit of paper what screws, connectors and other bits go where
Offer up new motor
Installation is the reverse of the abov eprocedure.
Turn on oven
Reset clock
Invite me round to dinner.
XX, August 2015
