Hi Clare, it sounds like some of the jets are blocked and the black could be soot from poor combustion.I would not use the hob and contact your manufacturer for a corgi gas engineer to call and repair it.
All the best.
FOXY
September 2008
I can answer this question...
my gas rings are making my saucepans black what can I do?
howtomendit.com for free repair help, information and advice.
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