Like all tools, an IR thermometer needs to be used properly.
I found that mine gave inconsistant results, even though I used black tape as a target.
Then when I looked more logically, I discovered that there was a parallax problem where at close distances, the laser target wasn't the same spot that the IR was reading. The dot might be on the pipe, but the IR is pointing at the wall behind the pipe.
If yours allows continuous readings while the trigger is pressed, try holding it sideways and scanning across a hot pipe. On mine ( Maplins £30 ) at a range of a couple of inches, the temperature reaches a peak reading when the laser dot has passed the pipe and is shining on the wall.
I now scan across a small target and look for the peak. It's much more reliable.