My heater is a.pro 155 it worked fine all last year but I got it out of my storage area for use this winter. It will start an run for about 15 seconds and trips the reset on the unit. What would make this happen. - don't know if it matters but this unit is several years old I'm gonna guess at least ten years old.

I have repaired many kerosene space heaters in the past. The number one problem that I see is everyone expects the heater to just come on every winter when they plug it up. But usually it does not. It's been sitting in storage collecting dust. And then you hear them say "It worked fine last year". If everyone would just do this at the end of each winter and you are ready to store your heater, (Drain the fuel & clean your tank out). Check your filters and replace if needed. It is that simple. When you need it, do not put the same fuel that you have in a can or barrel (from last year) in the heater. Discard the old fuel properly & just purchase some fresh fuel and start off fresh. If you use the old fuel that was left in the heater or can/barrel, you are just looking for trouble. If you fire the heater off with the old fuel, you are just filling the heater with problems. Water is the problem. The fuel tanks/cans, ect. sweat during the hot months and it all settles in the bottom. Inspect your fuel before using it. Look for water/trash that has settled in the bottom. Discard as needed. You will be nice and warm instead of having heater problems when your freezing & needing heat. Just remember "start off fresh".