Went to a call for a Bosch electric dryer not heating. I did the standard checks, including checking the air flow at the outlet on the house. It was ‘pretty good’ using my calibrated hand. I disassembled heater assembly, expecting a tripped TCO (thermal cut out), and surely enough it was tripped. So we had an overheating at some point.

Next I checked the heater thermistor, it was near spec and while it had some lint on it, it wasn’t excessive, so I didn’t think that was an issue. Hmmm. Let’s look at the heater. Ah ha!

Found it! A massive build up of fine cotton lint within the coils of the heater ribbon. Took apart heater canister to expose the heater ribbon, got the air blower out and blew out most of it. I used a fine flat head screwdriver and manually picked out the remaining.

If I hadn’t pulled off the heat assembly to inspect it, I wouldn’t have seen the blockage.