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Technical Focus: Sump Pumps

Sump pumps are designed to handle surface water and ground water (storm water) that accumulates around the building. They don’t handle sanitary waste liquids or solids. Sump pumps typically are installed when there is a risk of flooding grade or sub-grade areas. Exterior or interior perimeter foundation drainage systems may drain into a sump pump. Gutters and downspouts do not typically discharge into a sump pump system; this arrangement is risky because it brings outdoor storm water into the building. Downspouts should, of course, discharge above grade several feet from the house. Floor drains do not normally drain into sump pumps because the water may not be as clean as storm water.

Some houses need sump pumps because the slope of the land directs water toward the foundations. In other areas, sump pumps are necessary because of a high water table. The municipality may require sump pumps if the storm sewers are above the lowest floor level.

The presence of a sump pump is a warning for home inspectors. Most home inspectors agree that water is the Number One enemy of homes. The presence of a sump pump (or several sump pumps) increases the probability that the home has had or may have water problems. Look carefully for evidence of water problems, especially in sub-grade areas.

The Sump A sump pump system consists of a sump (tank) below floor level. It has one or more side inlets. The sump may be tile, steel, concrete or plastic, for example. Sumps should be at least 18 inches in diameter and 24 inches deep, ideally with a solid floor. Some sumps have gravel floors, which may work if they stay level. Sumps should have a cover to prevent people, pets and objects from falling in and to help keep radon gas, for example, out of the home. Covers should typically be flush with the floor surface.

The Pump The pump is in the sump. Pedestal pumps have the electric motor mounted above the sump. Submersible pumps have both the motor and pump at the bottom of the sump. In either case, there will be 120-volt electrical power and a float switch to activate the pump as the water level rises.

Electrical Sump pumps typically have 120-volt cords plugged into a conventional receptacle. The receptacle is typically a dedicated circuit. We do not want a sump pump deactivated because of a tripped breaker due to an overloaded branch circuit.

GFCI may not be required for sump pump receptacle.

All sump pumps should be electrically grounded and a Ground Fault Circuit Interrupter (GFCI) −protected circuit may make good sense, although codes may not require GFCI protection for sump pumps on a dedicated circuit. Many believe that the risk of nuisance GFCI tripping, which renders a pump inoperative, outweighs the safety advantages of GFCI protection.

Float switch wiring.

Sump pumps are typically controlled by a float switch. You may see two wires coming out of the sump pit to a wall receptacle. One wire is a piggy-back float switch. It plugs into the wall receptacle. The other wire is the power for the pump motor itself. It plugs into the back of the float switch plug. When water rises enough to lift the float, the float switch closes and starts the pump motor. The pump runs until the float drops enough to open the switch and turn off the motor.

Discharge Piping The discharge line is often polyethylene, PVC or ABS piping, although it can be any approved drainage piping material. Flexible hose is not a good material. Sewer odors are not an issue because we are dealing only with storm water. So, unlike sewage ejector systems, there is often no vent piping.

Codes now require a check valve on the discharge side, although we see many installations with no check valve. The purpose of the check valve is to prevent water in the discharge pipe from flowing with gravity back into the sump when the pump shuts off. Some sump pumps have an integral check valve.

A union is typically installed between the pump and the check valve. This allows for changing the pump without having to cut the discharge pipe. Where the pipe discharges into a storm sewer system (rather than to daylight), a manually operated isolating valve may be provided. Again, we rarely see this.

Sump pump pipes might discharge:

  • into a storm sewer or combination sewer (Most municipalities do not want sump pumps discharging into a combination sewer due to the unnecessary load that creates on the sewage treatment system.);

  • into a ditch;

  • onto the ground, well away from the home;

  • into a French drain (gravel pit below grade); or

  • out through a hillside (to daylight) if the ground slopes down away from the house.

Discharge pipes often are buried just slightly below grade and should slope continuously down away from the house. Low spots may lead to blockages and, in cold climates, the water may freeze, blocking the pipe.

Additional Protection Because sump pumps are not tightly sealed and only handle liquids, they are far less expensive than sewer ejector pumps. Because they play an important role in preventing flooding, many people keep a spare pump on hand. In some cases, the sump is large enough to house two pumps. The redundancy of two pumps reduces the risk of a flood.

Because storms often include power outages, sump pump systems may have battery backup power or may be powered by a generator. High-water-level alarms or no-electrical-power alarms can help prevent flooding. There also are water-operated sump pumps that can be driven by water pressure from the house supply plumbing when the power is out. These need high city water pressure and have limited capacity. They don’t work on homes with wells because well pumps do not work when the power is out.

Testing A Sump Pump The usual test for a sump pump is to lift the float as though the water level was rising to verify that the pump and motor work. Note: There is an electric shock hazard here because we have electricity and water together. Many inspectors use a voltage detector to ensure that the pump casing and controls are not electrically live before testing. We recommend using a wooden stick or other insulator to raise the float.

In some cases, you may not be able to remove the sump pit cover to access the float switch. A less reliable test is to unplug the pump wire from the piggy-back float switch and plug it directly into the receptacle. The pump motor should start. Once you verify that the pump motor works, unplug it quickly so you do not risk burning out the pump or motor.

Most home inspectors only test sump pumps if there is water in the sump. Running a pump with no water can damage the pump. However, even if there is no water, many inspectors lift the float switch briefly to ensure that the motor turns over. The inspection report should document any limitations.

Checking The Discharge Point Most home inspectors do not verify that water comes out at the discharge point. There is often not enough water in the sump to do this and the discharge point is not always readily accessible. Again, the limitation should be documented.

COMMON PROBLEMS Inoperative There is a risk of flooding if the sump pump is not operable. The sump may not work for several reasons:

  • a defective float switch system

  • a lack of electrical power

  • a seized pump

  • a burned-out motor

Excess Noise or Vibration Noise or vibration may be caused by a worn pump or motor with worn or damaged bearings. This often suggests that the pump is near the end of its life. There also may be foreign material in the pump, pedestal or discharge pipe.

Short Cycling or Running Continuously Short cycling or running continuously may shorten the life of the pump. Pumps may short cycle because of the following reasons:

  • The sump is too small.

  • The float switches are set incorrectly.

  • The sump is re-filling quickly after the pump empties it.

Pumps may run continuously because of the following reasons:

  • There is a control problem.

  • The float switch may be defective.

  • A float may be stuck and may not drop when the water level drops. In this situation, the pump may burn out or shut off on thermal overload.

  • There is water pouring into the sump continuously. There is a risk of flooding if the pump just barely keeps up with the water coming into the sump.

  • The discharge line is obstructed or disconnected. The pump may be operating properly, but the water may not be carried away.

If the pump runs continuously, check to see if the pump is running with the sump dry, water is not being moved out of the sump or water is flowing into the sump at a significant rate. If the pump is running continuously, it becomes more important to find the discharge point. That way, you can assure yourself that water is moving properly through the discharge pipe.

Debris in the Sump or Clogged Sump Sump pits are often collection points for debris. If silt or other foreign material gets into the pump, the pump may be destroyed. At best, it won’t move water as freely as it should. A clogged pump may run continuously without moving any water.

Sump Damaged If the sump pit is damaged, dirt may get into the sump. This will clog and possibly ruin the pump. Sump walls may be broken, rusted or collapsed.

Discharge Pipe Problems If the discharge pipe does not work effectively, water won’t be cleared from the sump and flooding may occur. Water should be discharged far enough away from the building that it won’t find its way back. The photo below shows a pump discharge immediately adjacent to the building at grade level. The water accumulates against the foundation wall and finds its way back into the sump. This creates a cycle that doesn’t get rid of any water and often results in flooding.

Cover Missing, Damaged, Rotted or Not Secure A missing or weak cover is a safety hazard. Children may fall into the sump. Objects may fall into the sump, obstructing the intake or fouling the float switch mechanism.

Pedestal pumps may have the float switch wires hung up on the cover. This can prevent the pump from running.

Conclusion Sump pumps are inexpensive devices with a critical role. They are an important part of a home inspection. The inspection report should explain the importance of the pump to clients. We recommend quarterly inspection and testing of sump pumps.

Alan Carson is President of Carson Dunlop, which is the creator of the ASHI@HOME Training Program, the Home Reference Book and Horizon Inspection Software.

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