Hi, im using a HIH-4030 but when i plug it in it gives a constant value no matter what i do, blow on it etc, using a volt meter it shows the same voltage on output and input, so that means no change is occurring can anyone help or suggest what could be wrong?

If the output is greater than about 3.8V (100% Relative Humidity) that probably indicates a wiring problem. It might be that the +ve pin is shorted to the Out pin or the -ve pin is not connected to Ground. Check your board for shorts and opens. Check your wiring for shorts and opens.