An old gas grill cleaning method was to cover the cooking grates with aluminum foil, turn the grill to high for 20 minutes, let it cool, and then simply brush off the ash. The foil holds the heat from the gas burners under the grates and reduces virtually everything to a fine dry ash that can be easily cleaned up.
Negative Impact of Cleaning Technique
While it sounds like a great idea, most modern grills simply cannot handle the heat from this approach. When most gas grills were made with heavy cast-iron parts, this wasn't a problem. Today it is. A modern grill firebox is often made of stamped steel and burners are intended to be consumable parts that wear out and can be replaced.
The intense heat created by this cleaning process can warp cooking grates, crack ceramic igniters and cause metal fatigue in the burners. Worse, the captured gasses can combust, gas lines and hoses can melt and the temperature inside enclosed carts can exceed the safe temperatures for storage of propane tanks.
Grill Manufacturers Opinions
The major grill manufacturers have issued statements that warn consumers to avoid the aluminum foil cleaning practice due to safety concerns. Weber cautions that this method "...could trap gas and become a fire hazard and blocking the airflow causes very high heat that can damage valves, burners and supply lines that may make the grill unsafe to use." As a safe alternative, they recommend preheating the grill (with no foil) on high for 10 to 15 minutes to burn off all residual food before grilling.
Similarly, Char-Broil warns that "it’s simply a bad idea to clean any grill in this manner...Blocking off the grate can overheat the entire firebox, and force heat into areas not necessarily designed for excessive heat."
Several other manufacturers have similar comments. Unfortunately, some reputable media outlets still point to the foil incineration method (as it is sometimes called) as the best way to clean a dirty gas grill. Since manufacturers warn against it, the gas grill's warranty may be voided if the grill is damaged by this process.
If anyone is advocating this method of cleaning a gas grill, do not follow the advice — even if they claim to have used it successfully. It's possible that a grill may accept this treatment once, twice or even more often, but eventually the chances of destroying the grill or causing a serious accident are very high.