Best thing is get a long lighter, like for fireplaces or fireplace matches and see if the flame is disturbed at the head, checking for leaks. If nothing is leaking then recheck all nuts and bolts in 100 miles. Keep an eye on for any bluing or yellowing. What kind of pipes and are they chrome or black. Did you wipe all fingerprints off before fireing up and torque bolts and did you use new gaskets?