Level of DifficultyDifficult
Time to do repair15 - 30 mins
Age of ApplianceMore than 10 years
Fixed it eventually with part PS470049 ('M' Series Ignition Coil Kit). See separate story.
The flame sensor did not fix it but read on for info on how to replace this part. Before replacing this part, I should have read another posting in a different web site about the ignition coils: if you see a red glow inside the burner unit but the flame does not come on, then the problem is likely to be with the coils, not the flame sensor. However since some users here had solved the problem by replacing the flame sensors, I figured I'd try it. The setting for "More dry, less dry" never worked either so maybe this would fix two problems at once.
This dryer is a stacked front loader sitting on top of our washing machine. Opening the little front door (lower left side) is easy once you figure out that a little screw below needs to be removed. I almost broke the door trying to pull it open. The sensor is attached to the side of the flame area cylinder. It was hard to remove both the screw and the part itself from the slots as it's very springy. In fact when I finally removed it, it dropped to the base of the unit and sparks went flying as one of the electrical clips touched the metal (ground). Tip: first disconnect the electrical lead coming from the back of the unit to the ingnition block and later I used rubber gloves just in case. (I could not access the plug/outlet in the back). I installed the new part easily, though I was confused by the electrical leads: the white wire connects to the lead that has a red plastic dot on the side, but I think that must be a mechanical part and not a (wrong) marking, while the red connects to the other lead. Anyway, I connected it the same way I found it and put it back. Reconnected the other electrical wires and closed the door.
This did not fix the problem which turned out to be with the gas valve coils: as they get old, they turn off the flame when they get hot, even though the dryer keeps on turning. To read how to replace that part, search for comments under part number PS470049 ('M' Series Ignition Coil Kit). I don't know whether replacing the flame sensor is going to fix the "more dry-less dry" function, will have to see. Still, this website is great. Our dryer is a Westinghouse bought in 1991 (almost 20 years old!) and with this fixes it's just like new.