Hi everyone, I'm new to this forum and new to welding. I recently bought the Titanium Flux Core 125 unit from Harbor Freight. I used it a few times with no problem, but the last time I used it I could not get it to arc no matter where I put the ground. I went back to HF and swapped it for another unit. When I tried again I got the same results. I then tried on an old rusted angled metal I had and it did spark the arc. I don't understand why it's working on that and not others.  Any thoughts?