Chris Green was thinking very hard :
You need to turn the knob *and* press the trigger on mine. Then when
it has lit you can use the knob to adjust the flame.

Same with my blowlamp, not that make. Squeezing the trigger, should
produce a definite click and the click fires the piezo igniter. Not
click, then try a match to ignite it, but there should be the sound of
gas from the jet. If not, the trigger is not opening the valve, or the
valve is blocked.