I'm gonna push back on this one. Checking the vent first sounds smart until you burn a $90 service call pulling a dryer out and finding a clean vent and a dead heating element anyway, which happens plenty. Vent clogs usually show up as long dry times or the dryer getting hot but not drying clothes, not a total no heat shutdown. A six year old electric dryer with no heat at all points straight at the element, the fuse, or the thermostat way more often than a clogged line. I've seen packed vents cause overheat trips, sure, but that's usually after 15 or 20 minutes of running, not right away. You did what most of us would do, tested the machine because the machine was the thing acting up. The real lesson here isn't check the vent first, it's ask the customer how long dry times have been and whether the outside flap is opening before you load the van. Half these diagnosis shortcuts people preach online only work when you already know the answer.

Mark your leader with tape so you know where the gap starts next time.