I have changed the heat element, but still have a problem. The problem is every time we use the tumble dryer it heats for a few seconds then the heat goes and runs cool.

The tumble dryer is a CL 311 white knight.

What can the problem be?

MRSNOTUMBLE- DID you check the heat protector on the duct where the heating eleme
Nt is :: also check all the vents for lint and the outside vent door for freedom of opening, they get so the vent flaps get sort of bent or a wasp has built a nest on the vent;; Check the outlet hose for kinks or bends and for lint build up ;; To check the HEAT OROTECTOR -
#1- IF you have a VOLT-OHM meter, SET it to RX1 scale::IF you don't you can get one in the elect. dept. at Lowe's or home depot.pretty reasonable, just get one you can test up to and includeing 250 VOLTS;; TO TEST the protector ,remove the back of the dryer and set aside, NOTE UNPLUG THE POWER CORD FROM WALL:: NOW where the heater element is ,the duct it is in ,look and you will see a small black object with two or three wires going to it ; REmove one of the wires and clip the one prob to the terminal you took the wire off ,now clip the other meter probe to the other terminal , IF THE METER READFS ( ZERO ) THE PROTECTOR IS GOOD <IF THE METER READS HIGH IT IS DEFECTICE <REPLACE );; #@ TO TEST THE THERMOSTAT - REMOVE BOTH THE WIRES ,now clip the meter probs to the terminals ( METER SHOULD STILL BE SET THE SAME ) TURN the thermostat to ANY SETTING EXCEPT ( FLUFF DRY ) :: IF METER READS ( ZERO ) THERMOSTAT IS GOOD< IF IT READS HIGH IT IS DEFECTIVE : REPLACE :: Don't FORGET TO REPLACE ALL THE WIRES YOU TOOK OFF << I HOPE that this solves your problem,IF not come back to this post and holler ;; HAVE A HAPPY NEW YEAR AND GOD BLESS <STAY SAFE:: F.B.E.