Renault Megane Scenic 99 1.6?

The Red to bBue rotating dial on my heater is making no difference to the temperature coming out of the vents.It is permanently hot.
Crimping one of the water pipes into the matrix under the bonnet allows cold air to flow.Is there a shut off valve for the hot water or is a flap sticking do you think......cable off maybe. How is the water/heat flow controlled
Many thanks