Points to note on the above answer: If the fuse was bad, then the motor that turns the drum would not rotate. A typical problem that causes tumble dryers to stop heating up is the thermal overload cut-out devices. These are safety devices, and are some times "single-shot". That is, if they operate, and shut off the heating element, then they need to be replaced, usually as a pair along with the thermostat (they look very similar). The other common fault is that the heating element fails. However, if the thermal cut-out was the problem, LOOK FOR A CAUSE. If it is a condenser drier, check the condenser box is not clogged with lint/fluff. TD1947
If it's a gas dryer, (and the vent is clear) you have one of two parts bad—the igniter, or the valve coils. Both are easy to replace, and if your dryer is older, you might want to replace them both, since they have about the same lifespan.
When the coils (they are not heaters, they are electric magnets that open the gas valve) get old, they stop working after they heat up (the electrical flow through them actually heats them up a little) so they often will work at the very beginning of a load, but only for about 5 minutes, then they stop working, and the dryer is just cold air for the rest of the cycle. If you notice that your dryer (after being off for a few hours) will actually heat up in the beginning, but won't stay hot, it is the valve coils. They are a snap to change.
The igniter is basically the same principle as a car cigarette lighter. It gets glowing hot when you turn on the dryer, then if the coils are working they open the gas valve, the gas hits the igniter and "voom" you hear the gas light. If the igniter breaks (and usually when they break, you can see the crack) the electrical flow is interrupted and the coils don't energize to open the gas valve.
If you have an electric dryer, it is most likely the element.
One other thing... As is stated above, there is a thermal overload fuse inside. If your vent is plugged and the heat can't escape, the thermal fuse will blow and your dryer won't heat until you change the fuse (and hopefully clear the blockage).
Should the only problem be that no heat is being permitted, there are two inline devices permitting the power to pass to the heating device (either electric or gas). Electric dryers have a curly heating wire going around the door opening. You won't see it unless you are to unplug the power cord & unfasten the front & side enclosure assembly, at the back of the unit. Pull the three sides forward away from the dryer body. The coil is to be inspected that it is continuous and without a break and there will be surface mounted bare metal flat round fuses usually with two wings/metal screws to anchor the fuse to the metal front frame of the unit. The fuse can be tested for continuity (if it will carry an electrical test charge across/through itself). The only other cause would be disconnected wires to the control dial or a bad temperature dial. Good luck and write down any wires by color disconnected during the disassembling adventure. What I didn't mention wires could be burnt and not continous, you will notice a black burn spot at that point!
Check your vent and make sure it's not stopped up. If it gets stopped up, then the dryer will get too hot. Most dryers have a safety thing that will burn up and stop the dryer from over heating, if the dryer gets too hot. That way nothing will catch on fire. You might have to replace that safety thing, sorry not sure what the name of it is, I don't know if its the heating element or just a safety switch.
This problem can be occurred due to many of the reasons. This is possible that your dryer is having some technical problem. While finding the reason of this problem you must not neglect the importance of the fuse because this is possible that the fuse of the dryer is not in good condition and that is why you are facing the problem with your dryer. There can be some kind of breakage inside the fuse and if this is so then replace the fuse with a newer one. If your fuse is working well and it is in good condition then check the temperature switch. It is possible that it is out of order or might be having some other problems. You can either fix the problem or can replace the switch. You can check the switch with the help of the VOM; if the reading does not change then this is possible that the switch has been gone out of order or bad. The third possibility is that the thermostat goes out of order.
Sometimes it happens that the heating coils suffer from some problem and that is affecting process of heat production. Some kind of damage with the timer can also cause the problem.
This answer helped me a lot. I was having the same problem with my dryer, it would spin but not heat. Sure enough the fuse was no good and it's fixed now. That saves me a ton of money because I was getting ready to buy a new one. Thanks!
The first thing that comes to my mind is the heating element. It could be that the heating element doesn't work any more and that might be why it runs, but doesn't get hot.
