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Problems with Gas hob

Currently have an oldish smeg 4 burner gas hop. Recently it has not been putting gas through. Will cut out then work half an hour later or not at all for a while. Has cut out during cooking. Not the gas bottle as have tried two. Would like someone to look at it, and if simple fix do it, but if its more involved will also replace the cook top at the same time rather than having to pay for that to be done later. Would prefer a simple fix now though obviously $$$ wise.