In most cases, only one spring breaks or wears out at a time, and you can get away with replacing just the failed spring. But this is a little like replacing old car tires one at a time. You'll get the best performance if all the springs are new and have the same strength. Extension springs are replaced individually, making it more tempting to replace just one. With torsion springs, you have to disassemble everything to replace either spring, so it makes sense to swap out both springs during the repair.
11.2a Raise the garage door slowly. Check the door balance. If you have the correct springs the door should stay down when closed, half way when opened half way, and open when opened. If the door will drop to the floor by itself from the halfway point, add 1/4 turn of tension to each of the torsion springs. If the garage door won't stay on the floor, and if it pulls itself up when stopped halfway, close the door and remove 1/4 turn of tension from the springs.	

As mentioned, the only time you should attempt to open a garage door with a broken torsion spring is during an emergency. Otherwise, you should contact a service technician for emergency repairs. We provide same-day garage door service for people just like you who find themselves stuck and unable to move due to a faulty torsion spring. For prompt, reliable service any time of the day or night, please contact us.
Quite a few garage doors come with manual locks, especially older models, for added security for your house. These typically look like a knob or handle in the middle of your door with two bars running horizontally from each side. There may be a small button on the top or side of the handle that you can press to slide the bars across the doors, thus locking the garage door from the inside. It can be somewhat easy to accidentally hit that button, especially if you’re getting large objects out of the trunk of your car near the door.
The two main garage door operating mechanisms are sectional roll-ups or tilt-ups. Garage door repair services can fix single-car, double-car or RV-height doors. Your garage door may be made of wood, steel, aluminum, masonite, vinyl, fiberglass or another material. The type of garage door repair you need really depends on the type of garage door you have and the issue at hand. Garage door repair pros often charge a flat service call fee to diagnose the problem and provide an estimate. For customers who choose to have the repair done, the service call fee may be applied to the first hour of labor (including time to make the diagnosis). If your garage door is under warranty, the repair may be free of charge.
If you are not sure if your door had the correct springs, we recommend that you weigh your door using an analog scale. From my own field experience I would estimate that at least 10% of the doors have the incorrect springs on them. In addition to this, most manufacturers spring their doors using a 20 pound window. We like to improve the garage door balance.
The national average for garage door repair cost is between $80 and $110. Some of the factors that affect your garage door repair cost are the type of springs (most often torsion or extension), the size and weight of the door, and the door material. Many garage door pros will charge a service fee to visit your house and determine the problem. Often, the service fee includes a set amount of labor. One example of this is an $80 service fee that includes the first hour of work plus testing and inspecting your garage door and garage door opener, while another pro may charge $150 for the same standard service call.    https://m.youtu.be/Z_eZc-kh40c
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