agree emmie and barrie
no one should go near and fiddle with a gas cooker without a CORGI certification
My gas fitter rang up and said - I have found your gas cooker has been fitted with water return valves ( in case of a disconnection, the back pressure closes the pipe(*) and not gas return valves
and I squealed: "the pressures are radically different, the house is a static bomb! - it is only about 14 cms water for piped gas!"
and of course, that should never have been done
(*) lack of pressure if you think about it, and the water prssure is so high they will never get activated