How To Test A Dishwasher Flow-Through Heater

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Dishwashers provide a convenient way to clean your dishware so you’ll have more time for after-dinner socializing, but the appliance won’t actually accomplish this task quickly. In fact, the average dishwashing cycle will take two to three hours to complete and that doesn’t include the time it takes to dry the dishes. While all dishwashers will fill the tank and pump water through the spray arms to clean the dishware in relatively the same way, the drying process will vary depending on the model.

Some models will use a flow-through heater to assist during the drying cycle. If this component fails to function properly your dishes will still be dripping hours later when you were hoping to simply move them from the dishrack to the cabinet shelves without having to hand-dry them with a towel first. In this article, we’ll explain how you can test a dishwasher flow-through heater to determine if it’s working properly or not. Let’s begin with how a flow-through heater helps dry the dishes.

How a flow-through heater helps dry the dishes

As noted above, not all dishwashers are designed to dry the plates, bowls, glassware, mugs, and utensils in the same way. Many models, such as the KitchenAid Model KDTM704ESS dishwasher, use a heating element to heat the air inside the unit to dry the dishes; other dishwasher models, like those manufactured by Bosch, will rely on a flow-through heater to do the job.

Flow-through heaters are installed underneath the dishwasher

While heating elements are usually fully exposed on the base of the dishwasher tank surrounding the sump and lower spray arm, flow-through heaters are installed underneath the dishwasher as part of the circulation pump assembly and are hidden from view. A heating element may be used to heat the water during the wash cycle, but its primary job is to heat the air during the drying cycle. A flow-through heater, on the other hand, will operate throughout the dishwashing process to heat the water used during the wash and rinse cycles.

The heat generated by the final rinse cycle will dry the dishes

Dishwashers with flow-through heaters rely on the heat generated by the final rinse cycle to dry the dishes. The hot moist air will then exit through a permanent vent or through a vent in the door which is opened by a wax motor or solenoid. Some dishwasher models will have a vent fan motor to assist in drawing the air through the vent.

Testing a dishwasher flow-through heater

If your dishwasher’s water isn’t heating or the dishwasher is not drying the dishes properly, it’s likely the flow-through heater is malfunctioning. To help confirm this you can use a multimeter to test the flow-through heater for electrical continuity – a continuous electrical path present in the component – as well as determine if power is being sent to the flow-through heater.

You will need to uninstall the dishwasher to reach the flow-through heater

The flow-through heater is normally located on the sump assembly underneath the dishwasher. You will need to uninstall the dishwasher to reach the heater for testing. Here are some general instructions for uninstalling a dishwasher:

  • Shut off the power to the dishwasher to avoid electrical shock while you’re uninstalling the appliance.
  • Next, unthread the water supply line from the inlet valve (be prepared for some water to spill out).
  • Unthread the screw securing the junction box cover.
  • Unthread the wires nuts to disconnect the power wires and detach the grounding wire as well.
  • Remove the power cord wire strain relief nut so you can detach the power line from the junction box.
  • Disconnect the drain hose from the sink drain or garbage disposer and feed it through the cabinet.
  • Unthread the mounting screws securing the dishwasher’s mounting brackets to the countertop, cabinet, or floor.
  • You may need to raise the front leveling legs to lower the appliance.
  • You should now be able to gently pull the dishwasher away from the cabinet.
  • Tip the dishwasher back onto its rear panel. You will likely need to pull the base away from the tank or remove a bottom panel to access the circulation pump assembly and flow-through heater.

Testing the flow-through heater for electrical continuity

Once you have access to the flow-through heater, refer to the dishwasher’s wiring diagram to identify the heater’s input and output terminals as well as the designated ohms of resistance for those terminals. Rotate the multimeter’s range selection dial to the lowest setting for ohms of resistance. You’re now ready to begin testing for electrical continuity:

1) Disconnect the wires from the appropriate terminals.

2) Contact the black meter lead to the heater’s input terminal and the red lead to the output terminal.

3) Observe the multimeter display. If the meter display shows a result between 5 and 30 ohms of resistance the flow-through heater has electrical continuity and should be functional. However, if the meter display shows less than 5 ohms of resistance the heater is likely faulty and should be replaced.

You can also use the multimeter to test whether the dishwasher’s control board is sending the appropriate voltage to the flow-through heater in order for it to operate. To do this the dishwasher will need to be reinstalled.

Reinstalling the dishwasher

Once you’ve reconnected the wires to the appropriate flow-through heater terminals and replaced the bottom panel or base, you’ll be ready to reinstall the dishwasher:

  • Return the dishwasher to its upright position.
  • Confirm that the end of the drain hose is accessible through the cabinet wall.
  • Gently slide the dishwasher back into the cabinet.
  • Adjust the leveling legs if necessary to raise the appliance.
  • Rethread the screws to secure the dishwasher’s mounting brackets to the countertop, cabinet, or floor.
  • Feed the drain hose through the cabinet and secure it to the sink drain or garbage disposal (make sure the hose is elevated above the connection point).
  • Fully position the power cord strain relief in the junction box, securing it with the strain relief nut.
  • Join the appropriate power wires and grounding wire together, securing them with the wire nuts or screw as applicable.
  • Realign the junction box cover and thread the screw to secure it.
  • Reconnect the water supply line to the inlet valve.
  • Reposition any insulation, then realign the lower access panel or panels and secure them with the screws or fasteners.
  • Turn on the water supply.

Testing for voltage being sent to the flow-through heater

Since you may need to uninstall the dishwasher’s outer door panel to reach the control board, it’s best to leave the power turned off. Be aware that the control board could be located underneath the front of the appliance instead of behind the lower access panel or panels (if this is the case, wait to reinstall these panels until testing is complete). Once you’ve reached the control board, use the appliance’s wiring diagram to identify the terminals on the board that supply power to the flow-through heater. Set the multimeter to “Volts AC” and restore power to the dishwasher. You’re now ready to test for voltage:

1) Select a heated wash cycle and press start.

2) After the tank fills, contact the black meter lead to the control board’s neutral terminal and the red lead to the designated power terminal.

3) Observe the multimeter display. If the display shows close to 120 volts being sent by the control board, you’ll know the board is not the cause of the heater malfunctioning. However, if the control board is not providing sufficient voltage to the flow-through heater, you will need to install a new board to fix the problem.

Dishwasher Flow-Through Heater Testing

Explore Repair Clinic’s “Videos & Articles” for repair assistance

Accessing, testing, and replacing dishwasher flow-through heaters can vary significantly from model to model which is why Repair Clinic encourages you to explore the “Videos & Articles” section of its website to find dishwasher schematics and step-by-step guides to assist you. Included in this free repair content library are model-specific procedural videos such as this one showing how to replace a flow-through heater on a Bosch dishwasher (model SHE43RL6UC64) or this video demonstrating the proper way to install a flow-through heater on a Danby model DDW1899BLS1 dishwasher.

Fix your dishwasher with genuine OEM parts

Not all parts are created equal. While some websites sell lower-priced generic knock-offs, Repair Clinic carries only genuine original equipment manufacturer (OEM) parts. When fixing your dishwasher, don’t settle for anything but a genuine OEM part that is specifically designed to work with dishwashers built by Bosch, KitchenAid, Kenmore, Maytag, Samsung, GE, Frigidaire, LG, Whirlpool, and other top brands. To find a complete list of all OEM parts compatible with your dishwasher, enter the full model number of the appliance in the Repair Clinic search bar. Repair Clinic does same-day shipping to ensure you are able to fix your dishwasher quickly knowing the appliance will stay fixed.

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