AAS Thermo Fischer Scientific iCE 3000 series

We have used above mentioned instrument for metal Detection.We are facing problem while using Nitrous oxide and Acetylene gas combination. In Chromium and Silicon was tested we are using these gases. In this case we are not getting Absorbance while using the standard solution. We are checking the standard solution in other instruments it’s ok, other parts like Nebulizer and Gas inlet areas are good. But still we are not getting absorbance. We are consulting with service person they told Acetylene and Nitrous oxide combination the flame should be Red cone formation in without sample. But we are only getting Blue with mixed yellow color in without sample. Only red cone formation while the sample was injected. Sample also not getting absorbance. We are not getting correct solution. So please help me.