Most new appliances are energy efficient, too, saving you money in the long run.

DreamPictures/Taxi/Getty Images

Knowing when to replace or repair home appliances is one of the keys to getting the best value for your investment. Replacement parts for appliances are typically available for seven to 10 years after manufacture and sometimes for much longer than that. Parts availability isn't the only criteria you should take into consideration when evaluating a repair, though.

If your appliance is still relatively new, it may have warranty coverage for major components. Check the owner's manual for more information. The next step is to do a little recon. A friendly service department guru may be able to help you diagnose the problem for free over the phone. A loose switch can look like a complete system failure and end up being a five-minute fix.

Your appliance may just need a simple "wear item," like a belt or washer. Technicians often stock common replacement parts like these on their trucks, making this an easy, relatively inexpensive service repair. Another bit of good news is that these common wear parts can be easy to replace yourself. In fact, there are lots of locations on the Web that carry all kinds of appliance parts for weekend warriors determined to save a dollar or two. These sites often include troubleshooting tips, exploded parts views and links to parts sellers. It's a brave new DIY world out there, but does that mean you should keep repairing a clunker forever? Well, probably not.

Older appliances may look like a bargain because you've already paid for them, so there's a strong incentive to keep them running as long as possible. When that refrigerator or dishwasher was designed and built, energy conservation technology wasn't what it is today, though. Thanks to programs like Energy Star, a combined effort by the U.S. Department of Energy and the EPA (U.S. Environmental Protection Agency), it's almost guaranteed that a new major home appliance will use less energy than its older counterpart. This means a cost savings to you and a big bonus for the environment. You'll still have to spend some cash, but you'll experience a savings over the life of the new appliance. The cost of energy is going up, so the future potential energy savings associated with upgrading your appliances could be significant.

If after some research it looks like you'll need to make a service call to get your appliance repaired, take a good, long look at how much it's likely to cost. Repair companies can often give you a tentative diagnosis and estimate over the phone. If a repair will cost 50 percent or more of what you originally paid for the appliance, you're better off putting the money into a replacement instead. If the appliance has given you trouble in the recent past, include those previous charges in your calculations. When you start throwing good money after bad, it's time to call it a day.

Look on the bright side! Now that you're going to buy a brand new appliance, you've got an excuse to indulge in that remodel you've been thinking about.