I have a Hygena Gas Hob Model AHY 1110. The gas can be cut off by closing the cooker lid. The hinge is connected through to a gas regulating valve. The valve is sticking and with the lid up the gas is not coming through. It does eventually come through if I tap the assembly with a hammer! Do I need a new hinge assembly or a new valve/regulator? Where can I get the valve/regulator?