Gas rings have no gas and will not light / operate. There is gas available in the house (gas boiler still works) but no hissing sound when any gas ring is turned on. I have checked the supply valve at the meter and it is in the on position. I have also turned the electrical power off and then on again at the mains in case there is a master safety valve (of which there is no mention in the handbook) which need to be reset but without effect. I was cooking something on the gas ring when it ceased working.