I have the above and one oven ignites but won;t heat up i.e. flame does not grow bigger to increase heat. I cleaned out all the burner holes and have a nice blue flame. Physically blowing out the oven ignition flame instantly forces the sparker to relight so I'm thinking FFD is fully functional here?
What I have noticed, is the sparker (one with the ceramic coat) glows red hot after a few seconds in the flame. That doesn’t happen in the other oven (which works).
I reckon swapping the unit over would prove it but that's a bit too much like hard work for me right now. Can anyone else comment before I get the tool kit out?

Steve 'I've had my head in the oven' H, December 2008

Tony S you are a gentleman sir!

1 X easy fitted FFD from eBay later and now oven flame is fully functional again.

Many, many thanks :)

Steve 'I've had my head in the oven' H, December 2008

The ffd is a mercury vapour valve.When the oven flame lights on low it warms a rod which bridges the burner.This rod connects to a valve which should open up the main gas supply.If its not coming up to full gas the whole valve needs replacing

Tony S, December 2008