I recently inspected a home that the garage door would not fully open. The automatic opener appeared to be working and there were no locks observed on the door. This is a newer type of spring that is installed inside a metal tube. You may have seen them installed on newer homes. There are no visible springs over the door, just looks like a bar with cables attached to the ends. I released the automatic opener from the door and tried to lift the door manually. The door was heavy, indicating the internal spring is probable broken. On this type of system, you cannot see the damaged spring like the older exposed spring systems. This internal spring system is actually a pretty good idea. With the springs being inside the metal tube they are safer and are not exposed to dirt and debris. When exposed springs break they tent to break into two or more pieces and on rare occasions come loose and damage walls, cars and people.
I explained to the home buyer that they could have the spring replaced. The cost is typically around $200.00 to $250.00 to replace and would last on average three to five years. Most companies will only warranty the spring for a year. The other option is to replace the system with an external type spring that typically last ten to fifteen years and cost about $100.00 more to install. It appears the safety of the internal spring comes at the cost of reliability. The cost of converting the system over to an exposed spring does cost more up front, but will typically be less expensive in the long run.
If you are looking at homes to purchase, I would use caution when operating the garage doors. During home inspections I have seen several damaged doors due to people not realizing the door had been locked at the track or the spring is damaged and the full weight of the door is on the opener. The door either buckles or the opener gets damaged by breaking the chain, belt and/or gears.
My number one Home Inspection rule: Don’t operate anything until you have looked it over first.