What Does the High Limit Thermostat Do on a Dishwasher?

The dishwasher is a time-saving convenience since it liberates the homeowner from the drudgery of hand-washing dishes.

Dishwasher Water Temperature Guideline

The dishwasher water must reach high temperatures.The dishwasher water must reach high temperatures.
To effectively dissolve detergents and remove soils, the dishwasher water must reach high temperatures. However, excessively high temperatures can reduce cleaning performance. The high-limit thermostat is intended to keep the dishwasher interior from overheating.

Dishwasher manufacturers recommend water temperatures of 140 to 145 degrees Fahrenheit for optimal cleaning performance. As many household water heaters are set to 120 degrees Fahrenheit or lower, many dishwasher models are equipped with built-in heaters to boost temperatures once the water has entered the machine.

Risks of Overheating

Water that exceeds 145 degrees Fahrenheit may reduce the effectiveness of certain ingredients in dishwasher detergents. In addition, water that is too hot may not be able to effectively remove some types of food soil.

High-Limit Thermostat Purpose

The high-limit thermostat is a safety feature created to prevent the dishwasher from exceeding optimal cleaning temperatures. Some models are designed to stop the dishwasher from operating if internal temperatures reach 200 degrees Fahrenheit. Once the machine has cooled to 100 degrees Fahrenheit, the thermostat may allow it to begin operating once more.

Trouble With High-Limit Thermostat

If the high-limit thermostat is malfunctioning, your machine may not complete the wash cycle. If the dishwasher does manage to get to the rinse cycle, the machine might shut down during the drying cycle. To test the high-limit thermostat, turn off the circuit breaker that governs power to the dishwasher. Check the thermostat for resistance using an ohmmeter. An ohmmeterr is an instrument that measures electrical resistance in units of measurement termed Ohms. Gauging resistance is one way to measure how well a component conducts, or reacts to, electrical current. An ohmmeter shoots a current across the component and gauges the component's resistance to the current. You can find a meter at a home-improvement or hardware store. When testing the high-limit thermostat, look for a reading of 0 to 1 Ohm. If the reading falls outside that range, the thermostat needs replacing.

About the Author

D. Laverne O'Neal, an Ivy League graduate, published her first article in 1997. A former theater, dance and music critic for such publications as the "Oakland Tribune" and Gannett Newspapers, she started her Web-writing career during the dot-com heyday. O'Neal also translates and edits French and Spanish. Her strongest interests are the performing arts, design, food, health, personal finance and personal growth.