To simplify the troubleshooting process, please answer the following question: Does the FID initially light and then goes out? If the FID initially lights, a distinctive popping sound will be heard every time the instrument attempts to light the flame. When it is lit, the baseline will usually exhibit a large sharp spike (over 100 pA) that accompanies the popping (Figure 1). If the FID does not light, then it may be the result of another set of problems. Another way to determine if a FID is lit without depending on output signals will be holding cool glass (like the bottom of a beaker or edge of a mirror) over the outlet of the FID. Water will condense on the glass if the FID is lit.
Top: successful; bottom: lighting failed.