Folks everyone forgets about their dryer till it doesn't heat.
The biggest cause is dirt. This picture is of an electric dryer about 3 years old. This not only causes the dryer not to heat right it's a fire hazard, dust and lint is highly flammable.
It can cause the element to burn out the blower motor to quite and thermal fuses to go out. leading to larger repair costs.
Get them cleaned every 2 years, if you have pets every year.
A service call to clean can cost around 65 to 100 dollars. depending on the brand and company. but add parts and you start to get even higher costs. A heating element runs around $75 to 100 plus labor.,so now your around $200.
This is a dryer motor
Gas dryer burner. Leave a dryer running while you run up to the store. no house when you come home. This is highly Flammable.