· Michael Blair
A dryer that used to finish a load in one cycle and now needs two has almost always lost airflow rather than heat. That distinction matters because the airflow version is both the more common problem and the one that starts fires.
How a dryer actually dries
It heats air, passes it through the tumbling clothes to pick up moisture, and exhausts that humid air outside. The heat is only useful to the extent that air is moving, so a dryer with a perfect heating element and a blocked vent will run all day without drying anything.
The symptoms follow from that. Clothes still damp after a full cycle, the drum and the laundry room noticeably hot, the cycle running longer than it used to, and a burning or hot lint smell. That combination is airflow, not heat.
Where the restriction is, in order of likelihood
The lint screen, which everyone cleans of lint and few ever wash. Fabric softener and dryer sheets leave a film on the mesh that restricts air while looking perfectly clean. Run water over the screen; if it pools rather than passing straight through, it needs washing with detergent and a brush.
Then the vent duct, from the back of the machine to the exterior hood. Long runs, flexible foil duct, crushed duct behind the machine, and too many elbows all accumulate lint. The exterior hood is the other common one, where a flapper stuck shut with lint or a bird nest blocks the outlet entirely.
- Wash the lint screen, do not just pull the lint off
- Check the exterior hood flapper actually opens when running
- Replace flexible foil duct with rigid or semi-rigid metal
- Pull the machine out and check the duct is not crushed
- Clean the full duct run annually, more with pets or heavy use
Why this is the fire risk it is
Lint is extremely combustible and a restricted vent both accumulates it and raises temperatures inside the machine. Clothes dryers are a well-documented cause of household fires, and failure to clean them is the leading contributing factor.
A gas dryer adds a second hazard, because a blocked vent can push combustion products back into the house instead of outside. A dryer that has become slow is giving you notice, and it is one of the few appliance symptoms worth acting on the same week.
When it really is the machine
If the vent is confirmed clear and the dryer still will not dry, the usual culprits are a failed heating element or thermal fuse on an electric machine, an igniter or gas valve fault on a gas one, or a worn blower wheel. A thermal fuse in particular often blows because of a blocked vent, so replacing it without clearing the duct just blows the next one.
A drum that turns but produces no heat at all points at heating rather than airflow, which is a different diagnosis from the slow-drying pattern. That is the case where the element or fuse is the first thing to test.