LG Dishwasher Not Heating Water — Element and Thermistor Diagnostics

When your LG dishwasher fails to heat water, dishes emerge greasy, sanitize cycles fail to reach proper temperature, and overall cleaning performance drops significantly. LG dishwashers use a heating element mounted along the tub floor to raise water temperature during wash and rinse cycles. The control board monitors water temperature via a thermistor (NTC temperature sensor) and activates the element when temperature falls below the programmed target. Error code HE appears when the control board detects that temperature is not rising despite commanding the element on.

An important LG-specific distinction: the heating element on LG dishwashers serves the wash and rinse heating functions but does NOT provide heat for the drying phase. LG uses their proprietary Dynamic Dry system (air circulation plus automatic door-crack) instead of heated drying. This means a heating element failure primarily affects wash cleanliness and water temperature rather than drying performance.

Understanding LG's Heating System

Heating element: A resistive coil element running along the tub floor. On LDT/LDP series, it is partially exposed (not fully concealed under a stainless floor plate like some Bosch models). The element heats water to 140-155F during normal wash cycles and up to 160F+ during Sanitize cycles.

Thermistor (NTC sensor): Mounted in the sump area near the element. This sensor reports real-time water temperature to the control board. Its resistance decreases as temperature increases (negative temperature coefficient). At room temperature, LG thermistors typically read 50K-55K ohms; at operating temperature (140F), approximately 5K-8K ohms.

Control board relay: A relay on the main control board switches 120V AC to the heating element. The board decides when to heat based on thermistor feedback and the selected cycle's temperature profile.

Symptoms of Heating Failure

Cold water throughout cycle:

• Dishes emerge with greasy residue (grease cannot emulsify in cold water)
• Detergent pods may not fully dissolve (many require 110F+ to activate fully)
• Error code HE may display during or after the cycle
• Cycle duration may increase (control board extends heating time before giving up)

Partial heating (not reaching Sanitize temperature):

• Normal wash seems adequate but Sanitize option fails
• HE error appears only on Sanitize cycles
• This suggests the element has increased resistance (partial failure) — it generates some heat but not enough to reach the higher Sanitize threshold

No error code but water clearly cold:

• Thermistor may be giving false readings to the control board
• If the thermistor reports "hot" when water is actually cold, the board never commands the element on
• No HE error appears because the board thinks heating is successful

Diagnostic Procedure

Step 1: Confirm Water is Actually Not Being Heated

Run a Normal cycle. At approximately 15 minutes in (during the main wash heating phase), pause the cycle and quickly open the door. Touch the water at the tub bottom — it should feel clearly hot (not just warm). If the water is barely above the supply temperature, heating has failed.

Step 2: Test the Heating Element

1. Disconnect power at the circuit breaker
2. Access the element terminals either through the bottom of the unit (remove kick panel, 4 Phillips screws) or from inside the tub
3. Disconnect the wire leads from the element terminals
4. Measure resistance between the two element terminals: should read 12-15 ohms on most LG LDT/LDP models
5. If resistance is infinite (open circuit): element has burned out — replacement needed
6. If resistance is significantly higher than spec (e.g., 25+ ohms): element has partial failure — generates less heat
7. Also test for ground fault: measure between each terminal and the metal tub — should be infinite (any reading indicates a short to ground, which is a safety hazard)

Step 3: Test the Thermistor

1. Locate the thermistor in the sump area (near the element, small two-wire sensor)
2. Disconnect its wiring
3. Measure resistance at room temperature: should be 50K-55K ohms (approximately)
4. If available, heat the sensor gently with warm water and verify resistance drops predictably
5. Infinite resistance or fixed resistance regardless of temperature = failed sensor

Step 4: Verify Control Board Output

If element and thermistor both test good:

1. Reconnect both components
2. Start a cycle and allow it to reach the heating phase
3. With extreme caution (live circuit), measure voltage at the element connector: should read 120V AC when the board commands heating
4. No voltage at the connector during heating phase = control board relay failure

Step 5: LG Smart Diagnosis

Use the ThinQ app or phone audio diagnostic:

• Smart Diagnosis reports thermistor readings over time
• Can identify whether the board sent heating commands
• Reports actual vs. expected temperature curves
• Particularly useful for intermittent heating issues that are hard to catch manually

Root Causes Ranked by Frequency

1. Heating Element Failure (45% of HE Errors)

The element on LG dishwashers is exposed to thermal cycling (heating/cooling every cycle) and direct water contact. Mineral deposits from hard water can create hot spots where the element corrodes faster. Visible signs of failure include:

• Blistering or raised spots on the element surface
• Visible break in the element coil
• Discoloration (darkened sections indicating excessive localized heat)
• White mineral crust building up (can insulate sections, causing uneven heating)

2. Thermistor Failure (25% of Cases)

The thermistor fails in two modes:

• Open circuit: Board reads infinite resistance, interprets as extremely hot, never turns element on
• Fixed low resistance: Board reads constant "hot" temperature, never commands heating Both modes result in cold water without HE error (because the board believes temperature is correct).

3. Control Board Relay (15% of Cases)

The element relay on the board can fail from contact erosion (high-current switching over years) or from voltage spike damage (LG boards are sensitive to surges). Failed relay = no voltage to element despite correct board logic.

4. Wiring/Connection Failure (10% of Cases)

The high-current connections to the heating element can corrode or burn at the terminal spade connectors. Heat cycling causes expansion/contraction that loosens connections over time. Inspect connector terminals for blackening or melting.

5. Incoming Water Temperature Too Low (5% of Cases)

Not a dishwasher fault per se, but if household hot water supply delivers water below 100F (failing water heater or long pipe run), the dishwasher element may be unable to raise temperature to target within the allotted heating time. This triggers HE on some models.

Test: Run hot water at the kitchen sink until fully hot, then immediately start the dishwasher. If HE error disappears, the issue is supply water temperature, not the dishwasher.

Repair Costs

Prevention

• Install a water softener or use monthly dishwasher cleaner to reduce mineral buildup on the element
• Run the kitchen hot water tap before starting the dishwasher (delivers pre-heated supply water)
• Ensure the dishwasher is on a surge-protected circuit (protects the control board heating relay)
• Run Smart Diagnosis via ThinQ app monthly to monitor thermistor accuracy trends

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