How To Fix A Dishwasher That Won't Drain

Some models of dishwashers utilize a check valve as part of the drain sump. Within the check valve there is the piston and nut assembly. If your dishwasher is not draining water properly, the piston and nut assembly could be the source of the problem. This assembly is located on the bottom of the tub beneath the sump cover and is accessed by removing four screws. The piston and nut assembly should move up and down freely. When the piston is in the down position, it should form a tight seal. If it is not forming a complete seal, the dishwasher will not completely pump out the water and the piston and nut assembly will need to be replaced.

You should also check the body valve gasket to make sure it is fitting properly over the threaded portion of the piston and nut assembly and replace if damaged or worn.

All dishwashers will have a method to drain the water. Most models will have a single motor driven pump with two separate compartments, one for circulation and one for drain, each with its own impeller. Other types will have a separate drain pump and some will utilize the main circulating pump in conjunction with a drain solenoid and diverter valve or flapper. On models that use a separate drain pump you should check to see if there is any obstruction to the input and output of the pump and also verify that there is power getting to the pump motor during the drain portion of the cycle. If both check ok, then you should replace the pump and motor assembly.

On models that use a drain flapper and solenoid, again you should check for any obstructions and verify that the solenoid is getting energized and that there is continuity. Use a multi-meter to make these tests. Check that the linkage operating the flapper or diverter is moving freely and replace any defective parts. On models that have a two section pump, the drain impeller may be at fault. First, verify that the motor is running in the proper direction. If the motor does not run, then check for power at the terminals on the motor. If voltage is not present, then you should check door switches, timer or electronic control as a possible cause. If proper voltage is present, then the motor windings could be open. If the motor is humming, then the problem could be that the drain impeller is jammed or the motor could be seized. If the motor is seized, then the motor or motor and pump assembly will need to be replaced. The electrical checks can be made with a multi-meter.

Disassembly of the pump will be required to determine if the impeller is the problem. The drain compartment is typically located beneath the circulating compartment. Remove the lower rack, spray arm, pump cover and filter assembly to gain access. Inspect the drain impeller for damage or wear and replace if required. Also check that the food chopper is in good condition and not allowing large food particles to clog the drain outlet, and that both the chopper and impeller are turning freely.

Some dishwasher models will use a check valve in the drain outlet. The check valve is used to allow water to flow in one direction but will prevent the dirty water from re-entering the dishwasher. The valve is normally a rubber flapper that is located on the outlet port of the drain pump or housing. If you suspect that the drain hose has a restriction or if you find that waste water is getting back into the dishwasher tub, then the check valve is most likely the problem. The flapper valve should fully open during the drain portion of the cycle but should close the opening to the pump outlet when in the wash or circulation portion of the cycle. If there are no foreign objects restricting this action, then the check valve should be replaced.

Some older dishwashers may use a belt driven pump. If the belt has come off or is slipping then the pump that drains the dishwasher won’t function properly. Inspect the belt for signs of wear or stretching and replace if required.

Some dishwashers will use a mechanical timer to operate the cycles. The timer controls the main pump motor as well as the drain solenoid or separate drain pump motor if your model has that style. The timer is normally located in the control panel at the top of the dishwasher door. You will require a wiring diagram and schematic to identify the correct timer contacts that control the drain cycle. These can then be checked for continuity with a multi-meter and if defective then the timer will need to be replaced.

A dishwasher will not drain properly if it has a restricted or clogged drain hose. Restrictions typically appear most often at the outlet from the pump or drain housing where a check valve may be located, at the input to the household drain system or anywhere that a kink may have formed in the drain hose. If food debris has caused a restriction, then you should check the condition of the food chopper as a possible source of the problem. If the hose has developed a kink it should be replaced and the new hose should be supported well enough to prevent any new kinks from forming.