A. This is what is written in the Yalkut Yosef:
Skewers and grills that you broil meat on and can have chametz mixed into them periodically. Since there is direct contact without liquid in between to (consider it cooking) it needs to be burned and whitened out with fire until sparks fly out of the grill or skewer. Regular boiling won’t work for these items beforehand.
Post facto if you boiled them instead of burning them in fire, and you cooked or even broiled with them you can rely on authorities that it is kosher.
If you’re not sure if the items were used with chametz, boiling them is enough but it’s better to fire them as they may have been used with chametz.
With blessings of Success,