It's sometimes possible to detect a faint gas smell after you turn on your gas clothes dryer. It's at this point that the gas valve opens to release gas for the igniter to produce a flame required for heat. However, if the smell is stronger than normal and you can't find a leak in the dryer's main gas line, at least one of three burner assembly components might be defective.
Burner Assembly Components Overview
Your gas clothes dryer's three main burner assembly components are the igniter, gas valve and flame sensor. Each needs to operate properly to generate a flame used to heat the dryer. When you start your dryer, the igniter comes on, and the gas valve opens nearly simultaneously. Once the gas connects with the igniter, it ignites to produce a flame. The flame sensor detects the flame and shuts down the igniter.
Check your dryer manual to see whether or not your dryer has a glow or spark igniter. A glow igniter is a long metal rod that gets extremely hot, eventually becoming an orange-red color. A spark igniter initiates a spark to make a flame. Remove the dryer's main access panel so you can see the igniter. Turn the dryer on. Look for an orange-red glow or spark, depending upon which igniter type your dryer has. If there is no flame within 15 seconds, the igniter has likely burned out and needs to be replaced.
A bracket secures the igniter so that it connects efficiently with the gas. The bracket is made of a thin metal and attached to the dryer by a screw. It's possible for the screw to loosen and cause the igniter to wobble so that it's unable to connect with the gas as it's released from the valve. Consequently, a strong gas odor might be noticeable. If you turn on your dryer and see the igniter glowing or sparking yet no flame is generated, the igniter is likely out of alignment. You may be able to tighten the screw and realign the igniter; but if it's broken, you'll need to get it replaced.
Defective Gas Valve Seal
If you smell gas even when your dryer is off, the problem might be a defective valve. The valve should seal shut when your dryer is off so that gas isn't released. However, it's possible for the valve to fail over time and emit a small amount of gas into the air, whether or not the dryer is operating. Shut off the dryer's main gas line and contact a dryer repair specialist to evaluate the valve's condition. If it's not sealing closed, he'll likely recommend that you swap it out for a new one.