A dryer that tumbles but won't heat has lost only its heat source — most often a blown thermal fuse, a failed heating element (electric) or igniter (gas), or a half-tripped breaker.
Heat and tumble are separate systems. If the drum spins but nothing gets warm, the motor is fine and you're looking at the heating circuit: power supply, safety fuses, and the element or igniter. A clogged vent is also a frequent hidden cause because it trips the thermal fuse.
Check these in order. The first accounts for most cases.
Electric dryers use a double 240V breaker. If only half trips, the drum spins on 120V but the element gets no power — so it runs without heat.
A clogged vent overheats the dryer and blows a one-time thermal fuse as a safety cutoff. The dryer then runs with no heat until the fuse is replaced and the vent cleared.
Electric: the heating element coil burns out. Gas: the igniter weakens and won't light the gas valve. Either kills the heat.
A blocked exhaust vent restricts airflow and trips safety thermostats; a failed cycling thermostat can also cut heat.
Follow these in order. Stop as soon as the problem clears.
Cut power before any panel comes off. For gas dryers, also close the gas shutoff.
Fully flip the dryer's double breaker off, then on. A half-tripped 240V breaker is the most common no-heat cause and the easiest to miss.
Disconnect the exhaust duct and clear lint from the duct and the wall vent. A clogged vent is what blows the thermal fuse in the first place.
With power off, find the thermal fuse on the blower housing or heat duct and test it for continuity. No continuity = replace it (and clear the vent that blew it).
Electric: test the heating element for continuity; replace if open. Gas: watch the igniter glow — if it glows but gas never lights, the gas valve coils are likely bad.