--- title: "Flashback Behind the Grill Knobs: Flame at the Wrong End of the Burner" description: "Why a web in a venturi tube moves the flame behind the control panel, the sound and signs to know, closing the gas from a safe spot, and keeping the tubes…" url: "https://bbqgrillrepair.center/guides/flashback-behind-the-knobs/" date_modified: "2026-09-26" --- Gas, fire and food at the grill # Flashback Behind the Grill Knobs: Flame at the Wrong End of the Burner Gas grill flashback is flame burning at the front of a burner tube, behind the knobs, instead of at the ports under the grates, usually because spiders or insects blocked the venturi. Close the gas at the tank or shutoff only if you can reach it without passing the panel, step back, let the flame die and have the burners and valves checked. By [BBQGrillRepair.center technical team](https://bbqgrillrepair.center/authors/technical-team/) Published September 26, 2026 ## At a glance. Gas is meant to burn along the top of each burner, under the grates, well away from your hands. Flashback moves that flame to the front of the burner, into the space behind the control panel where the valves, the hose and the igniter wires live, and it is the one grill emergency that starts right beside the knobs you would reach for. Read the whole guide ### Most common cause A web or nest in the burner tube Blaze calls an obstructed burner tube the most common cause of flash-back. ### What you hear A whooshing, jet-like roar Blaze describes flashback by this sound. ### Where the flame sits Behind the control panel Lynx warns nests can cause a fire behind the control panel. ### Owner's check The venturi tubes, at least yearly CPSC asks for a yearly look for insects, spiders and food drippings. In this guide 1. What gas grill flashback is, and why it starts at the tube 2. Signs that flame has moved behind the knobs 3. The moment it happens: gas off from a safe spot, then step back 4. Keeping the venturi tubes clear through the year 5. Before the grill is lit again 6. Step by step 7. Questions ## What gas grill flashback is, and why it starts at the tube Each burner on a gas grill is a hollow tube. At its front end the valve sprays gas from a small brass orifice into the mouth of the tube, and the venturi, the narrow first stretch of it, pulls in air through an opening called the air shutter. Gas and air mix on their way down the tube and leave through a row of ports, where they burn as a steady blue flame under the heat shields. Gas grill flashback happens when that mixture cannot travel down the tube. Blaze's use and care guide explains that spiders and small insects spin webs or build nests in burner tubes, that the obstruction can cause a fire in and around the tubes known as flash-back, and that while it is not the only cause it is the most common one. The gas that cannot get past the blockage spills out at the front, beside the valve, and burns there. ### Why spiders and wasps pick the burner tubes A venturi tube is dry, dark and narrow, and on a grill that sits under a cover for weeks it is the quietest shelter in the yard. Lynx names the burners, venturis, valves and orifices as places spiders and insects like to nest and says a grill that has stood unused for a long time needs those parts inspected and cleaned before it is lit. Mud-building wasps and spiders do not care whether the grill is a cart model or a built-in head. Source: [Blaze — Professional Series Use and Care Guide](https://www.blazegrills.com/wp-content/uploads/Blaze-Professional-Grill-Manual.pdf) — Webs in burner tubes cause flash-back and are its most common cause; flashback has a whooshing, jet-like sound, turn off the burners; symptoms of nests are gas smell with yellow flames, low temperature, uneven heat and popping; inspect burner tubes before each use; burners must be seated over the valve orifice ## Signs that flame has moved behind the knobs The first sign is usually sound. Blaze describes flashback by its whooshing, jet-like noise, quite unlike the soft rush of a healthy burner. Its insect warning lists the other clues that a nest is choking a burner: a gas smell together with yellow burner flames, a burner that never reaches temperature, uneven heat across the grate, and popping noises. - A roar or whoosh from the front of the grill, below the lid line - Flame or glow visible in the gap under the control panel or around a knob - One knob, or the panel beside it, too hot to touch - Lazy yellow flame at the ports of one burner while the others burn blue - Melted or blistered knobs, or a scorch mark on the panel after cooking ### Wind can put heat behind the panel too Not every hot panel is a nest. Lynx explains that its grills draw air in at the front and vent hot gases out the back, and that wind blowing into the rear can stop those gases leaving, until the control panel and knobs become extremely hot. It suggests a wind break behind the grill and turning the grill so the prevailing wind does not blow into its back. Napoleon's manual likewise tells owners not to place a grill where strong wind comes from directly behind it. Source: [Blaze — Professional Series Use and Care Guide](https://www.blazegrills.com/wp-content/uploads/Blaze-Professional-Grill-Manual.pdf) — Webs in burner tubes cause flash-back and are its most common cause; flashback has a whooshing, jet-like sound, turn off the burners; symptoms of nests are gas smell with yellow flames, low temperature, uneven heat and popping; inspect burner tubes before each use; burners must be seated over the valve orifice Close on a faint flame below the control panel of a grill. ## The moment it happens: gas off from a safe spot, then step back The flame is fed by gas leaking past the blockage, so closing the gas starves it. On a cart grill that means the handwheel on top of the propane tank; on a built-in or natural gas grill it is the shutoff valve on the supply line. Close it only if you can reach it without leaning over or past the control panel. Blaze's instruction is to turn off the burners immediately, and where the knobs sit right in the flame, the tank valve or the shutoff is the safer way to do the same thing. Then step back and keep everyone away from the front of the grill. Do not pull the knobs, open the lower cabinet to look, or throw water at the panel. If the flame is out once the gas is closed, leave everything off. If fire keeps burning behind the panel, spreads to the hose or the cart, or you cannot reach the gas, move away and call 911. ### Why nobody reaches through the heat The space behind the knobs holds the manifold, the valve bodies and, on many grills, the hose and the igniter wires. Flame there is heating the very parts that carry gas. Reaching past it to turn a knob that may already be soft puts a hand and arm in the hottest spot on the grill for no gain, when the valve at the tank does the same job from a step away. Source: [Blaze — Professional Series Use and Care Guide](https://www.blazegrills.com/wp-content/uploads/Blaze-Professional-Grill-Manual.pdf) — Webs in burner tubes cause flash-back and are its most common cause; flashback has a whooshing, jet-like sound, turn off the burners; symptoms of nests are gas smell with yellow flames, low temperature, uneven heat and popping; inspect burner tubes before each use; burners must be seated over the valve orifice ## Keeping the venturi tubes clear through the year CPSC's grill safety fact sheet asks owners to check the venturi tube for blockage by insects, spiders or food drippings at least once a year, clearing it with a pipe cleaner or wire that pushes the blockage on through into the main body of the burner. Blaze goes further and says burner tubes must be inspected and cleaned before each use. Many makers now fit a fine screen over the air shutter to keep insects out: Napoleon puts one on each burner, and Weber's US owner's manual shows stainless spider and insect screens and asks for them to be kept clean, because lint on the outside can starve the burner of air. A grill coming out of its winter cover is the one most likely to have tenants. A few minutes with the grates and shields lifted, a flashlight and a flexible venturi brush, all with the gas closed and the grill cold, is the whole job for most owners. ### What stays in place during that cleaning - The valve bodies and the manifold behind the panel stay where they are. - The brass orifices are not unscrewed, drilled or swapped. - Air shutters that the maker set at the factory are not turned by guesswork. - A burner that is lifted out follows the manual's steps and goes back seated over its orifice. Source: [Blaze — Professional Series Use and Care Guide](https://www.blazegrills.com/wp-content/uploads/Blaze-Professional-Grill-Manual.pdf) — Webs in burner tubes cause flash-back and are its most common cause; flashback has a whooshing, jet-like sound, turn off the burners; symptoms of nests are gas smell with yellow flames, low temperature, uneven heat and popping; inspect burner tubes before each use; burners must be seated over the valve orifice; [CPSC — Safety Checks for the Grill (fact sheet, Publication 467)](https://www.cpsc.gov/s3fs-public/GasGrill_factsheet_2013.pdf) — At least once a year check the venturi tube for insects, spiders or food drippings and clear it with a pipe cleaner or wire, pushing the blockage through into the burner; [Napoleon — Built-In Series owner's manual (N415-0601)](https://www.napoleon.com/sites/default/files/products/N415-0601-Built-In-Series-Manual-RevH.pdf) — Do not locate the grill where wind can come from directly behind it; burners carry an insect screen on the air shutter; keep venturi tubes free from spider webs; [Weber — Spirit natural gas grill owner's manual (8653810, US)](https://digital-assets.weber.com/documents/8653810_062024.pdf?fm=pdf) — Burners are fitted with stainless spider/insect screens; debris on the outside of a screen can obstruct airflow, keep the screens clean ## Before the grill is lit again Heat behind the panel can do damage that does not show from the front: a valve seal baked hard, an igniter wire with cracked insulation, a hose softened where it passes behind the manifold. A burner that flashed back may also have been knocked slightly off its orifice, which Blaze notes must be avoided for proper operation. Each of those can turn the next lighting into a leak or a second flashback, so the burners, valves, hose and wiring are looked at before the gas is opened. Source: [Blaze — Professional Series Use and Care Guide](https://www.blazegrills.com/wp-content/uploads/Blaze-Professional-Grill-Manual.pdf) — Webs in burner tubes cause flash-back and are its most common cause; flashback has a whooshing, jet-like sound, turn off the burners; symptoms of nests are gas smell with yellow flames, low temperature, uneven heat and popping; inspect burner tubes before each use; burners must be seated over the valve orifice ## Where to stop Nobody removes a valve, unscrews an orifice, loosens a fitting behind the panel or tests for a leak with a flame after flashback. Once the grill is cold, book a visit so the burners are cleared and reseated, the valves, hose and igniter wires are checked for heat damage, and every connection is leak-tested before the gas is turned back on. Written by [BBQGrillRepair.center technical team](https://bbqgrillrepair.center/authors/technical-team/). Technicians who fix burners, igniters and pellet feeds on backyard grills, drawing on service calls and makers' manuals. Sources: [Blaze — Professional Series Use and Care Guide](https://www.blazegrills.com/wp-content/uploads/Blaze-Professional-Grill-Manual.pdf) · [Lynx — Professional Grill Care, Use and Installation Manual](https://assets.ajmadison.com/ajmadison/itemdocs/owners-manual-LYNX.pdf) · [CPSC — Safety Checks for the Grill (fact sheet, Publication 467)](https://www.cpsc.gov/s3fs-public/GasGrill_factsheet_2013.pdf) · [Napoleon — Built-In Series owner's manual (N415-0601)](https://www.napoleon.com/sites/default/files/products/N415-0601-Built-In-Series-Manual-RevH.pdf) · [Weber — Spirit natural gas grill owner's manual (8653810, US)](https://digital-assets.weber.com/documents/8653810_062024.pdf?fm=pdf) ## Step by step. Four steps, in the order worth doing them. 01 ### Close the gas at the source Close the tank valve or the gas shutoff, but only if you can reach it without passing the control panel. 02 ### Step back Move everyone away from the front of the grill and let the flame die once the gas is gone. 03 ### Call if it keeps burning Call 911 from a distance if fire stays behind the panel or reaches the hose or cart. 04 ### Leave it off Keep the tank closed and the knobs off until the burners and valves have been checked. For the heart of your home. ## Questions owners ask. ### Is gas grill flashback dangerous if it stops on its own? It can have damaged parts even when it stops. Flame behind the knobs heats the valves, the hose and the wiring, so leave the gas closed and have them checked before the next cook. ### How often should the burner tubes be checked for spiders? CPSC asks for at least once a year and Blaze asks for an inspection before each use. Always check after the grill has stood unused under a cover for a season. ### My grill has insect screens. Can flashback still happen? Screens make nests much less likely but need keeping clean themselves. Weber notes that lint and debris on the outside of a screen can block the air the burner needs. ### Why did only one knob get hot? Each burner has its own tube and valve, so a nest in one tube affects only that burner. The other burners can look perfectly normal while one burns at the wrong end. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://bbqgrillrepair.center/problems/) Gas or fire at the grill ### Grill Flashback: Flames Behind the Knobs or Under the Panel 6 causes, cheapest first Problem ### Grill Yellow Flame and Soot on the Grates 5 causes, cheapest first Problem ### Grill Uneven Heat: Hot Spots and Cold Corners on the Grates 6 causes, cheapest first ## When it needs a technician. The repairs on the right are where this guide ends when the checks do not settle it. ### Grill burner replacement Rusted, split or blocked grill burners cleared or replaced, their venturi necks freed of webs and nests, and every flame set blue and even. ### Grill cleaning and safety inspection A deep grill cleaning with the burners out, venturi tubes cleared, grease path scraped, gas supply leak-checked and every flame read before the season. ### Grill valve and regulator repair Stiff, leaking or unshuttable grill valves, worn knobs, tired regulators and cracked hoses replaced, with gas orifices matched to propane or natural gas. ## More in gas, fire and food at the grill. What to do when you smell gas at the grill, when grease catches in the firebox, when flame shows behind the knobs, and how hot grilled meat and poultry must be before it is safe to serve. [The whole section](https://bbqgrillrepair.center/guides/safety-and-food/) Gas, flame, grease and safe temperatures ### A Grease Fire in the Grill: Burners Off, Gas Closed, Lid Down If It Is Safe, Never Water How to tell a flare-up from a fire that will not stop, the order of the first moves, when it becomes a 911 call, and what to look over once the grill is cold. Gas, flame, grease and safe temperatures ### Safe Temperatures for Grilled Food: 145°F, 160°F, 165°F and a Food Thermometer USDA's minimum internal temperatures for steaks, burgers, poultry and fish, why a browned crust proves nothing, holding food at 140°F and the 2-hour limit. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Flashback Behind the Grill Knobs: Flame at the Wrong End of the Burner](https://bbqgrillrepair.center/guides/flashback-behind-the-knobs/)** **[Book a visit with BBQGrillRepair.center](https://bbqgrillrepair.center/schedule/)**