how can i fix my rangemaster classic 110 Dual fuel FSd ?

Typical parts.

Sensor alone:

http://www.rangemaster-spares.co.uk/classic/fsd-probe/product.pl?pid=1214329&path=174040

Complete flame failure device:

http://www.rangemaster-spares.co.uk/classic/flame-safety-device/product.pl?pid=532961&path=174040

This is only a guess at the most likely cause of your problem
If you do not feel competent to do the repair, get a qualified Gas Safe engineer to do it for you.

Check you are ordering the correct part. I do not know the exact model of your cooker.

Ensure you know how to reset the timer/clock before starting work

A manual is probably available from Rangemaster website or use Google to search online

Ensure the cooker is isolated from the mains before working.
Have a pen and paper and make notes of where screws and wires etc., go. Do not rely on memory

Have some some containers available for screws so they can be grouped according to from where they came

HTH
November 2015

If there is a fame failure thermocouple, this may have failed.

XXX
November 2015