I am not getting any output PPM for any gas measured. Please help me with my problem. I'm trying to read the following gasses:

H2 gas concentration:0.0000 PPM

CH4 gas concentration:0.0000 PPM
C2H50H gas concentration:0.0000 PPM
H2 gas concentration:0.0000 PPM
NH3 gas concentration:0.0000 PPM

using the following code:

float gasdata = mics.getGasData(H2);
Serial.print("H2 gas concentration:");
Serial.print(gasdata,4);
Serial.println(" PPM");

gasdata = mics.getGasData(CH4);
Serial.print("CH4 gas concentration:");
Serial.print(gasdata,4);
Serial.println(" PPM");

gasdata = mics.getGasData(C2H5OH);
Serial.print("C2H50H gas concentration:");
Serial.print(gasdata,4);
Serial.println(" PPM");

gasdata = mics.getGasData(H2);
Serial.print("H2 gas concentration:");
Serial.print(gasdata,4);
Serial.println(" PPM");

gasdata = mics.getGasData(NH3);
Serial.print("NH3 gas concentration:");
Serial.print(gasdata,4);
Serial.println(" PPM");
delay(1000);

but somehow I'm getting 0 ppm for all the gasses. Please help me.