The grates on a stove, which one uses throughout the year for cooking, require "kashering" before Pesah to become permissible for use on Pesah. The stove is used for pots that often contain Hametz (and, on some rare occasions, one might have placed bread directly on the grates), and therefore they may not be used for Pesah unless they undergo proper kashering. This is done by thoroughly cleaning the grates and then either immersing them in boiling water, or pouring boiling water on them directly from the kettle. As long as the water is boiling, pouring the water directly onto the grates (after they have been cleaned) suffices for rendering them kosher for Pesah.
The same applies to oven grates. One must remove them from the oven, thoroughly clean them, and then either immerse them in boiling water (which is often not feasible because of their size) or pour boiling water on them. Electric hot plates and blechs can also be kashered in this fashion. They should be thoroughly cleaned, and then one pours boiling water on them directly from the kettle.
One who wishes to be stringent should purchase new stovetop grates and oven grates, and a new blech, for use on Pesah. This is certainly preferable, though it is perfectly acceptable to kasher these items in the manner described.
Tablecloths that have been used for Hametz may simply be run through the washing machine, on a hot water cycle, or dry cleaned, and then used for Pesah. No further measures are necessary to kasher tablecloths for Pesah. If one has a vinyl cloth that he uses over his table, it is proper to pour boiling water on it to kasher it for Pesah.
Summary: Although it is preferable to purchase new stove and oven grates for Pesah, one may kasher them for Pesah by thoroughly cleaning them and then either immersing them in boiling water or pouring boiling water on them directly from the kettle. The same applies to electric hot plates and blechs. Tablecloths need to be simply washed in a washing machine to be rendered kosher for Pesah, but if one has a vinyl table cover, he should pour boiling water on it to kasher it for Pesah.