Before blaming any part, a technician checks whether hot water is even reaching a dishwasher that isn't heating water, then tests the three parts of the heating loop: the heater, the temperature sensor that reports to the control, and the control that switches the heater on. You can help by noting how the dishes feel at the end of a cycle and whether cycles have been running unusually long.
Before the visit
- •Model and serial number. On many dishwashers the label is on the side or top edge of the door, visible when it's open.
- •What you notice. Cold dishes, wet dishes, cloudy glasses or cycles that run much longer than usual.
- •Error codes or flashing lights, written exactly.
- •When it started, and whether the water heater was changed or turned down.
- •Access to the kitchen sink cabinet and the dishwasher's lower front panel.
Safe pre-checks:
- Run the kitchen faucet until the water is hot before starting a cycle.
- Confirm that a heated wash or heated dry option was selected, if your model has them.
- Don't touch the heating element in the tub; it can stay hot after the cycle ends.
The checks, in the usual order
| Step | What's tested | What it rules in or out |
|---|---|---|
| 1 | Hot water temperature at the sink and at the dishwasher's inlet | Rules out a cool supply from the water heater or a long pipe run |
| 2 | Cycle and options selected | Rules out a setting that skips heated wash or dry |
| 3 | Stored fault codes | A heater or sensor code points straight to that circuit |
| 4 | Heater resistance, with power off | An open heater can't make heat |
| 5 | Temperature sensor (thermistor) resistance | A sensor reading wrong can keep the heater off or end heating early |
| 6 | Voltage to the heater during the service-mode heat step | Shows whether the control is actually switching the heater on |
| 7 | Control board | Considered once the heater and sensor test good but get no power |
Whirlpool's service manual for its 18- and 24-inch ADA built-in dishwashers shows how this works on one design. Its heater fault appears when the water doesn't reach target temperature after 90 minutes, and separate codes flag a temperature sensor that's open or shorted. The no-heat steps check the heater's resistance, run the service-mode step that powers the wash pump and heater, and look for line voltage at the heater; no voltage there points to the control board. The manual also lists a supply water temperature of 120°F for that design.
Other brands flag the same three areas in their own way. Samsung's dishwasher error code page lists a heater error and a temperature sensor error, plus a water supply error for a dishwasher that isn't getting water at the pressure or temperature it needs. It also tells owners not to reset or clear a code before troubleshooting it, which is why writing the code down comes first.
Tools you may see
- •Thermometer, for the water at the faucet and in the tub.
- •Multimeter. The heater and the thermistor are checked with power off. On the Whirlpool model above, the thermistor reads about 10,000 ohms at 77°F and drops as it warms; other models differ, so the tech sheet is the reference.
- •Service mode. On that model, a button sequence at power-up runs fill, wash and heat, the dispenser and drain one step at a time.
Questions you'll probably be asked
- •Are the dishes cold, or warm but wet?
- •Have cycles been running longer than they used to?
- •Does the kitchen faucet take a long time to run hot?
- •Was the water heater replaced or its setting lowered?
- •Have any lights flashed or codes appeared?
- •Do you use the heated dry or sanitize option?
What the findings usually mean
- •Cool water arriving at the dishwasher: the supply is the issue, and the dishwasher may be working normally.
- •Heater reads open: the heater circuit has failed, either the heater or its wiring.
- •Sensor reads open or shorted: the control can't tell the water temperature, so it may skip or cut heating.
- •Heater and sensor test good, but no voltage reaches the heater: the control board.
- •Long cycles with no code yet: the control may still be waiting for the water to warm before it flags a fault.
- •Dishes warm but spotted or filmy: a water-quality issue more than a heating one.
If the cycle stops partway instead of finishing cold, see what a technician checks when a dishwasher stops mid-cycle.
Sources
- •Service Manual, Whirlpool 18" and 24" ADA Built-In Dishwashers (W11187658), Whirlpool
- •Samsung Dishwasher Is Displaying an Error Code, Samsung
Good to know: Running the faucet hot before a cycle is the one pre-check that can change the result right away.
To have the heating checked, call TrueFix San Antonio at (210) 401-3007 about dishwasher repair.