invalid operands of types 'float()' and 'double' to binary 'operator<='

This is my code.

while(getPeso <= 0.8)  // In this line is the error.
        {
            Serial.print("Sirviendo");
        }

float getPeso()
{
    float Sensor =  analogRead(pinSensor);
    float Voltaje = (Sensor * 3.7)/4095;
    return Voltaje;
}

You are comparing a pointer to a function to a smiley face. That's never going to work.

If you want to call the getPeso function and use the value returned, then you need the parenthesis on the end.

getPeso is a pointer to the getPeso function
getPeso() calls the function and let's you use the value returned.

Nice smiley !

Please put code tags around your code by using the </> icon and post your whole program so that the problem can be seen in context.

codetags added