The Natural Philosopher has brought this to us :
No oven I have ever encountered behaved like that

Likewise and obvious if you turn the control's setting. Set it to a mid
setting, watch the flame and when it hits that setting the flame
significantly reduces to a low level. Turn it up a notch, the flame
goes to maximum. Turn it down the flame reduces to minimum, until the
cools down to the new setting. All done by capillary tube and expansion
inside the tube, controlling the jet's supply of gas.