DFrobot Flame Sensor always at 0

Hi everyone

I'm unexperienced when it comes to arduino so please bear with me.

I have this sensor

I've made this connections in my arduino mega 2560, where i've connected the data port to analog A0.

And finally i ran this code:

void setup() {

void loop() {
  int sensorValue = analogRead(A0);

No problems so far, the problem comes when i open the serial monitor window and get always 0, with or without flame.

I've tried switching analog inputs, tried 3.3V and 5V supply from board and still nothing. Tried 2 different sensors and nothing.

Can someone help me please? Thanks for your attention.