Frustrated-please help !!!!!!!!!!!!!!

Question

having difficulty maintaining heat in the ideal range on the gauge and cooking food up to temperature. we have to finish things in the oven. Gauge stays in the warm range. We do know that the gauge does work because we lit behind it with a lighter and it moves fine up to hot range. once the charcoal is in white ash range, we add more charcoal like it says in the instruction manual and open little door. We can see the flame but the gauge never gets up to ideal range. please help