my Gas Oven (Cannon Winchester) see in detail below:-?

The pilot light on my gas oven lights up but will NOT increase the intensity of the flame when I turn the knob on full power. The pilot light just sits there in low heat and won't increase. This is a Cannon Gas Oven It's a winchester model bought in late 1990s.

My gas engineer is not farmiliar with cookers but recons Thermocoupler ??? not sure really. Help please cuz I don't want to thro it away cuz it functions well as a cooker, just the oven bit is annoying. Ta very much.