[Bill Nicolo]

Our gas-heated clothes dryer will heat up occasionally but not each time the heating ignitor element lights. I first cleaned out the vent system, which was somewhat but not completely obstructed. I removed the front panel, put the dryer on the highest heat setting, and started the dryer. After a few seconds, the ignitor lights up, and after a second or two the flame will light. There is a good solid flame until the dryer reaches desired temperature, and then the flame shuts off. After about a minute, the ignitor lights again in an attempt to re-light the flame, but the flame doesn't re-light. After a few attempts like this, the flame will again re-light. It is as though it re-lights on every fourth or fifth attempt, greatly extending drying time.

What do you think?

[AmpDraw]

This is most commonly caused by that hot surface or "glow bar" igniter being bad. Yes it heats and glows, but as it heats up it drops in its resistance, thus allowing more current to be able to pass through it, which eventually allows the gas valve to open up. When these start going bad they do still glow, however never heat up enough to allow enough current to pass so you see them glowing but nothing more other than intermittent operation.

You'd need an amp clamp type meter to properly test this igniter, check around one of the two wires connecting it, the hot surface igniter's are fairly standard and require about 3 Amps of current passing through them before the gas valve will open up. If this checks out good then Its safe to assume everything else is ok since you do clearly see it calling for heat, in that case its possible your gas valve is bad. The hot surface igniter is your most likely culprit here though, like 90% chance even though you do see it glowing.