Gutters systems can last 20-30 years, but that doesn't mean they'll never need repairs. They may spring leaks over time and the spikes that hold them to the fascia board can work themselves loose. They may also need adjusting if the water is no longer draining well even when there are no obstructions.
Companies that install new gutters often also make small repairs on existing gutters -- though you should expect to hear a sales pitch arguing that new gutters are the way to go. If you just want yours repairs, make several calls and get estimates. This can also be a good job for a handyman, who may be more likely to give you a good price than someone who is motivated to sell you a new system.
So when you search Angie's List to find a service provider in your area, be sure to check both categories -- "gutter repair" and "handyman."
Install yourself or hire?
Hanging gutters isn't rocket science -- but there is some science involved, not to mention skill, so make sure you're up to the job. Remember, if you do a bad job it will be obvious to everyone who walks past your house.
Gutters need to have a slight incline or "fall" to allow water to drain towards the downspout -- typically about half an inch for every 10 feet. However, it should appear to the observer to follow a perfectly straight horizontal along the roof line. Professional installers can manufacture lengths of gutter on the spot to match the precise length of your roof line. This means no seams to join together.
If you install gutters yourself, you will be buying them in sections from the hardware store and joining them together to stretch the length of your roof. This means there will be visible seams that can leak. You also run the risk of creating a wavy effect over several sections while trying to span 40 feet or more of roof line. Even if this is not noticeable to the naked eye, you will create places where water pools and does not drain. One advantage professional installers have over you (in addition to their skills and experience) is that they can manufacture sections of gutter on-site to match the exact length needed.
If you are considering doing the job yourself, first add up the total footage of gutter you need, including downspouts. Don't forget to include the number of endcaps, elbows, spikes and so on. Go to the hardware store and figure out how much it will cost for the materials. Remember that this will be a two-person and two-ladder job. If you'll need to buy or rent ladders, add that to your cost.
Before you start buying materials, call three installation companies and get estimates from them. Naturally, this will be more than your materials-only total, but you can then decide whether the difference is worth it to have the job done professionally. Search Angie's List to find installers in your area that have received the best recommendations from past customers.