The firebox is the part that makes a grill a grill. When the floor goes, drips miss the cup, flames lick the tank cabinet, and electrodes have nothing solid to bolt to. Paint is not steel.
Three kinds of rust
- Surface bloom on thick porcelain-enameled Weber boxes and stainless lids. Ugly. Wire-brush loose scale, dry, high-temp paint if you care. The box is still a box.
- Scale you can push a screwdriver through. Structural. A furnace-cement “patch” or a pop-riveted plate lasts until the next heat cycle lifts it — then you have a loose plate in a fire.
- Perforation at stress points: lid vent, hinge screws, electrode rail, grease opening. A torn hinge will not hold a lid. A rusted-free electrode rail will not hold a spark gap.
Triage
- Cold, tank off, grates and plates out.
- Daylight test: shine a light from the cabinet up. Stars of light in the floor are holes.
- Poke test along the grease trough and the back wall. If the driver sinks, stop treating this as a cleaning project.
- Shake the lid. Play at the hinge is a lid problem; play in the box metal is a box problem.
- Inspect the electrode rail and burner retainers. If those mounts are gone, new tubes have nowhere honest to sit.
What you can reasonably repair
- A replaceable cook box sold as a spare for a current, expensive series (some Genesis and premium built-ins). Search the manufacturer and BBQGuys for cook box plus the exact model. If the box is sold, costs less than a new grill, and the cart and gas train are good — that is a repair. Look up the price; we do not invent it.
- Lid-only rust-through on a cart whose box is fine: a lid search, same rule.
- Pellet barrel with a rusted grease drain but a sound pot and barrel: sometimes a drain part exists. A rusted firepot is usually a pot replacement, not a barrel replacement.
What you should not repair
- Box-store aluminized boxes with daylight. There is rarely an official replacement box at a rational price.
- Home-welded patches on thin steel — they warp and leak.
- Fire cement in the grease path — it blocks the drain and starts a fire.
- A box that already had a grease fire. Heat-softened valves and blistered cabinet paint are not visible from the lid. Replace the appliance.
Decision
- Sound box + cheap consumables = repair.
- Daylight + three other parts = replace.
- Use the worksheet and the flowchart above.
- Not a welding manual. If you are a welder and the box is thick steel, you already know. If you are not, do not learn on a gas appliance over a propane tank.
Use the replacement-grill search above if you decided the cart is done.