Series № 1 of 4 Patio & Pour
Yellow Flame After Winter: Webs and Needles in the Venturi
The grill lit, but the flame is tall, soft and yellow instead of short and blue, and it leaves soot. After a wet season under a cover, the likeliest cause is not a failed part but something living in the tubes that feed the burners.
Written by
Hollis Yamada
- Role
- Service technician — refrigeration and cooking
- In the trade
- 21 years in the trade
What is a venturi, and why does it decide the colour of the flame?
The venturi is the open-ended tube between the gas valve and the burner. Gas leaves a small orifice at the valve and shoots into the tube, drawing air in with it; the two mix along the tube and burn at the ports. Viking grill burners have an air shutter at that inlet end, which sets how much air gets in.
The mixture decides the colour. With enough air, a gas flame burns blue with a firm inner cone. Starved of air, it goes soft, tall and yellow, lays soot on whatever it touches and runs cooler than it should. So a yellow flame is a question about air before it is a question about parts.
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Why does it turn up after winter?
Viking’s own manuals warn that spiders and insects nest in grill burners, venturis, orifices and valves, and they ask owners to have those areas inspected at the start of every season. A grill that stands covered through the wet months is dark, dry and still inside — exactly what a spider looks for.
Around Woodinville there is a second source. Tall firs drop needles and bark scale onto patios all winter, and wind works them under a cover and into any opening it finds. One web across the mouth of a tube can be enough to upset the mixture; a nest can close it.
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What does a blocked venturi look like from the patio?
- One burner, or one side of the grill, burns yellow and lazy while its neighbours stay blue.
- Soot builds on the underside of the grates above that burner.
- The burner is slow to light, or its flame is uneven along the row of ports.
- In the worst case, flame appears where it should not: at the front, behind the control panel.
That last sign is not a colour problem. Viking warns that a blocked tube can start a fire behind the manifold cover, damaging the grill and making it unsafe to use.
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What can you check yourself, safely?
With every knob off and the grill cold, lift out the grates and whatever sits under them, and shine a flashlight over the burners and into any opening you can see without tools. Webs, egg sacs, needles and nests are often visible from there.
Check that nothing inside is lined with foil; Viking’s troubleshooting notes that foil interferes with airflow and causes low heat. Look along the gas hose for cuts, cracks or chafing. Note which burner burns yellow, and at which setting.
That is where the owner’s share ends. Lifting burners off their orifices, moving air shutters and clearing tubes is gas work.
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What happens on the visit?
The burners come out and each venturi is looked down with a light and cleared. Ports are opened with fine wire rather than anything that could snap off inside them — Viking’s manual rules out toothpicks for exactly that reason. Each burner goes back with its inlet seated over its orifice, the air shutter is checked, and every burner is lit and watched from high to low.
On a 5 Series grill, whose igniters glow rather than spark, the igniters are watched as well. If the flame stays yellow with clean tubes, the next suspects are the gas pressure and the orifice, and a manometer answers that.
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Does a yellow flame always mean a blockage?
Not always. Viking notes that a few orange tips are normal where the air is dusty or grease is heavy, so a mostly blue flame flickering orange at the tips is no cause for concern.
A grill converted between propane and natural gas without the matching orifices can also burn yellow, and so can a burner set back slightly off its orifice after cleaning. A flame that is weak but blue on every burner at once points away from the tubes altogether, toward the gas supply.
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How do you keep it from coming back?
Have the burners, venturis, orifices and valves inspected at the start of each season; that is the habit Viking asks for, and the one that matters most. Let the grill dry before covering it — the manual is firm that a damp grill never goes under a cover. Keep the drip tray clean and in place, and drain it after rain if the grill stood uncovered.
Lighting the grill now and then through the idle months also helps: a burner that is used disturbs whatever is moving in.
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Follow-ups
Can I still cook on the burners that burn blue?
Not until the yellow one has been looked at. The burners share a manifold behind the control panel, and a blocked tube is the kind of fault that can put flame where it should not be. Turn every knob off, close the supply, and ring Woodinville Viking Repair on (425) 321-3414 to have the tubes cleared.
Will a grill brush or a garden hose clear the venturi?
No. A brush cleans the grates and the outside of a burner, and water in a gas tube or valve is a new problem, not a cure. Viking's manual clears ports with a straightened paper clip and debris through the air shutter, with the burner out. That is the visit's work: Woodinville Viking Repair, (425) 321-3414.
How often should the venturi tubes be checked?
Once a season at least. Viking asks owners to lift the grilling racks off at the start of every season and check the burners, venturis, orifices and valves for obstructions, and to have them inspected after any long idle spell. After a winter under a cover, that means spring. If you find webs or a nest, Woodinville Viking Repair, (425) 321-3414, clears them.