Why does your fry pan warp when is gets hot?

If your fry pan warps, you are using too high a heat.

Always start pans on a cold stove. Turn up the heat to medium, never up to high. Leave the pan to heat for a few minutes: it will reach a temperature high enough to cook most foods, and you can increase the heat as you need to.

More pans and foods are ruined by using too high a temperature than any other cause.

Most moderately-priced pans are not designed to be used on high heat. The heavier the pan, generally speaking, the greater heat it can take, but always refer to the manufacturer's instructions when buying a pan, and make sure you season it before first using; the manufacturer's guide will tell you how to do this.

Pans or pots placed on a heat source (stove top) get heat in one area. If the burner is the same size as the bottom of the pot it will all heat more or less evenly. But if it is heated in just a small area of the base of the pan you can get the heated metal expanding while the metal farther to the edge stays more constant. The expanding metal will sort of 'bubble up' in the middle.

But if you place a pan on high heat with nothing in it, or something too small, this can still happen. If you are having this occur, you are probably heating the pan to a higher than necessary level.

This is controlled some by the pans that have a thicker, copper or aluminum, base. These metals 'spread' the heat more evenly.