DEAR TIM: My crawl space and basement is prone to flooding during periods of heavy rain. The sump pump sometimes vibrates and fails to work. When it does work it often does not keep up with the incoming water. What might be wrong? Is there a backup system available? What sized pump should work well for an average house? Shelly T., Grosse Point, MI

DEAR SHELLY: Sump pump failures are the bane of many a homeowner. I have seen thousands of dollars worth of damage caused by just 2 to 3 inches of water in a basement. Often the failure of the pump can be traced to simple installation mistakes. High quality sump pumps can operate for years without a major malfunction. I know as I have installed hundreds of them.

The leading cause of failure in most sump pumps tends to be a switching problem. The switch of a sump will often fail to turn on because the pump has shifted inside the sump basin. The float that operates the switch can lodge against the side of the sump basin. Furthermore, it is not uncommon for a piece of debris to interfere with the action of the pump switch. Check to make sure your pump switch and float arm assembly move freely.

The vibrations and inability to pump on occasions can almost always be attributed to pump air-lock. When a sump pumps turns off, the water in the discharge line between the pump and the check valve drains back into the sump. If the pipe between the pump and the check valve is solid, the air in the line will compress the next time the pump tries to empty the sump basin. This compressed air can prevent water from leaving the pump. A 3/16 inch vent hole in the side of the discharge pipe inside the sump solves this problem. Check to see if your discharge line inside the pit has this hole. If it does, make sure it is not clogged.

Your sump basin may be too small. All too often people use a simple 5 gallon bucket as an inexpensive sump basin. This is inadequate. A residential sump basin should have a minimum inner diameter of 18 inches. It should be at least 22 inches deep. Small and narrow sump basins cause switching failures and more frequent pumping cycles.

A sump pump backup system might be a good idea. Often flooding occurs when sump pump needs are the greatest. A soil saturating rain storm may cause a localized power outage. Water flowing into your sump activates the switch, but there is no electricity to pump the water. Powerful battery operated sump pumps solve this problem. These pumps get their power from standard high performance automotive batteries. They come with alarms that tell you if the battery is low or partially discharged.

If you don't like batteries and live where you have city water, you can get a backup pump that operates on regular water pressure. These pumps will usually get you through the emergency until regular power is restored. You may use less than $1.00 worth of water to save thousands of dollars in damage to your belongings.

If your current pump has a 1/3 or one half horsepower rating, you should be OK. Higher horsepower pumps will pump more water. Look for pumps that have cast iron or heavy metal housings. Cast iron can dissipate heat buildup much better than a pump with a plastic or thin metal housing. Remember, price is usually an excellent indicator of quality. Higher priced pumps often have better parts!