The answer is often, yes! Many times your dryer vent becomes so restricted that it causes a failure within the appliance. So, yes, it is often due to your vent; and, yes, it is often your appliance. The lack of heat is a direct sign of an appliance problem (typically the heating element), but oftentimes is indirectly due to restricted ductwork causing the appliance failure in the first place. I’ve heard many customers recount that the warranty company warned that they would not cover the repair again unless the homeowner got the dryer vent professionally cleaned—otherwise the appliance can just keep failing requiring repair after repair. That is dangerous, and could be a prime situation for a fire to start.