Stop troubleshooting and follow gas emergency advice. In Great Britain, call 0800 111 999 from a safe place.
What the observation means
Do not operate electrical switches, create a flame or try to locate the leak yourself. A knob that appears to be Off does not make the smell harmless. Follow the emergency service's directions.
A useful next step
Tell the responder where the smell was noticed and the appliance involved. Do not wait for an ordinary repair appointment or repeatedly turn knobs to investigate. Routine service discussion can follow after the immediate safety concern is addressed.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.