test the push button for open and faulty .However see this causes too.Clogged Vent
If your dryer seems to run forever, it could be because of a clogged
vent or internal ductwork. Your dryer may have an automatic cycle that
turns off the dryer when the clothes are dry. It does this with a
special thermostat or moisture-sensing system.
Normally, this is what happens during an automatic cycle:
The thermostat tells the dryer to heat until the interior of the dryer reaches a pre-set temperature--say 135 degrees.
When the dryer reaches the pre-set temperature, the thermostat tells the
timer to begin advancing. (If there's a moisture sensor, the timer
advances only if the moisture content of the clothing is low enough.)
The timer advances until the interior cools, then the thermostat tells
the timer to stop advancing, and tells the dryer to start heating again.
This cycle continues until the clothes are dry. But...if the vent is
clogged, the dryer may never reach the proper operating temperature, so
it doesn't send the signal to the timer and the dryer continues to run
indefinitely, even if the clothes are completely dry. To fix the
problem, clean the vent and/or internal ductwork.
Your dryer's heating element may be partially burned out. If it is, your
dryer still heats, but at such a low temperature that it takes three or
four times as long to dry the clothes. If the element is partially
burned out, replace the heating element
You can check for an ohm reading but will need to refer to the service
manual for proper reading. This sometimes on the tech sheet located
somewhere on the dryer. Usually between 9-13 ohms.
Although this isn't a common problem, one of the thermostats that
controls the temperature in your dryer may break and cause the dryer to
heat poorly. If so, you need to replace it. The thermostat is usually a
small, round, black device mounted to an oblong steel plate. The plate
is mounted to the internal ductwork . This thermostat usually has four
wires going to it. Check the 2 terminals that are opposite each other
and are the closer together of the 2. These 2 terminals should have
continuity. If not replace the thermostat.