What Stu said is true - but it is possible.
Dismantling mine (its a freestanding one) is as follows
1. Remove all the trivets etc from the top of the hob
2. Remove the small screws that secure the burners to the hob. On mine, there are 2 per ordinary burner and 4 on the wok burner.
3. Slide the oven etc out from the wall. On my oven the gas cock is now exposed. Turn the gas off. Turn off the power to the oven, usually at the main board as well.
4.On the back of the hob there are two small brackets, one at either end of the oven. Undo the screws that hold the brackets to the oven frame, you can also undo the ones that hold the brackets to the hob but they are marginally harder to get out and replace.
5. The back of the hob should lift, the front is held by two Dzus pop fasteners. The front should "pop" off and you can then remove the whole top in one hit. Move the top to somewhere safe.
5. At this point, there are live electrical connections exposed around the main control and temperature control. If you haven't done this, then turn the power off!.
6. The fan is underneath the gas manifolds. Using the correct sized spanner, loosen the nuts on each gas control (5 for mine) and then spin the nuts off by hand. Give each manifold connection a gentle shake and it should come loose from the gas taps.
7. Undo the 4 screws that hold the burner support assembly and you can swing the whole assembly to one side. Your can also remove the connections to the gas ignitor and the whole assembly can be put to one side.
8. At this point you can remove the air ducts around the fan. The front of the duct is secured by 3 screws that can be got at by opening the oven door. They are just visible beneath the control panel.
- The fan is now exposed and you can work on it as required.
Replacement is to just reverse the above steps. Note, you don't need to be a gorilla about the nuts on the gas pipes. Just nip them up nicely.
Tony
March 2012