Abstract: A valve (100) for controlling gas flow for a gas heating which allows, as different embodiments, (1) A gradual and smooth transition from high flow to low flow. This is achieved by a rotatable control means (108) wherein the valve body or control means has a taping groove (134) on an annular path intersecting with a port to allow variation in flow rate as the control means rotates. (2) The ganging together into modular form of several valve units with the inlet ports forming a common inlet manifold. (3) The control means, at least, is a plastic, eg nylon. (4) The switching to off from either high or low flow is allowed. But the switching from off to on is directly to high flow.