It may not be broken.
When lighting this type of heater the flame is only visible during the lighting process which warms the catalytic material. After you release the lighting button or knob, whatever you have, the flame goes out but heat should continue to radiate from the pad. You may see a slight red glow in the dark, but nothing in normal light.
Hold your hand near it and feel for heat.
When lighting , I usually wave my hand at it to move the flame across the pad more evenly.
Rick Davis 1602 TAC TN-2 K8DOC
61 tradewind, plus a few others
13 Ram 2500 TD
99 Dodge TD 577K miles