LG Dishwasher Overflowing — Inlet Valve and Float Switch Diagnostics

An overflowing LG dishwasher represents both a water damage risk and a specific system failure that LG addresses with error code FE (fill error/overflow). When the water level inside the tub exceeds the maximum threshold, LG's control board immediately terminates the fill cycle, activates the drain pump continuously, and displays FE. If the overflow reaches the base pan, the polystyrene float sensor also triggers error code AE simultaneously. An overflowing dishwasher demands immediate attention because water can rapidly damage flooring, subfloor material, and adjacent cabinetry.

LG dishwashers regulate water level through two independent systems working in parallel: a pressure-based water level sensor (air trap in the sump) that measures fill height electronically, and a mechanical float switch in the base pan that serves as a backup overflow protection. Both must fail for a true overflow to reach the floor — the pressure sensor controls normal fill termination, while the float switch is the safety backup that should catch any overfill condition.

Understanding LG's Water Level Control

Primary level sensing (pressure sensor/air trap): Located in the sump area, this sensor uses a sealed air chamber connected to the tub. As water rises, it compresses air in the chamber. A pressure transducer converts this air pressure into an electrical signal that the control board reads as water level height. When the signal reaches the programmed fill level, the board de-energizes the inlet valve solenoid (5220FR2006H), stopping water flow.

Secondary protection (base pan float): A polystyrene float sits in the base pan beneath the tub. If water ever reaches the base pan (from any source — overfill, leak, or condensation accumulation), the float rises and triggers a micro-switch. This immediately signals the control board to stop all water intake and activate the drain pump. This system triggers AE error code.

Water inlet valve (5220FR2006H): A solenoid-operated valve that opens when the control board energizes it (120V AC) and closes when de-energized. It relies on the solenoid's spring-return mechanism to seal completely when power is removed.

Why an LG Dishwasher Overfills

1. Inlet Valve Stuck Open (40% of FE Errors)

The solenoid valve relies on a spring and rubber diaphragm to seal when de-energized. Over time, mineral deposits from hard water can build up on the valve seat or the diaphragm, preventing complete closure even after the board removes power.

LG-specific inlet valve behavior: The inlet valve on LDT/LDP models includes a built-in mesh screen at the water inlet port. When this screen becomes partially clogged, water pressure increases at the valve seat during operation. This increased pressure can force water past a weakened diaphragm seal even when the solenoid is in the closed position.

Test:

1. Stop the dishwasher and turn off the water supply valve
2. Open the door — if water continues entering the tub after supply is shut off, there may be pressure residual (wait 30 seconds)
3. If water continues well after supply shutoff, there is backflow from the drain side (check valve issue)
4. Turn supply back on but leave the dishwasher powered OFF — if water enters the tub with the unit off, the inlet valve is mechanically stuck open and needs immediate replacement

2. Pressure Sensor Failure (25% of Cases)

If the air trap chamber leaks, fills with water (losing its air pocket), or the transducer fails, the control board receives incorrect level readings:

Air trap filled with water/debris: The chamber must contain trapped air to function as a pressure sensor. If soapy water or debris enters the chamber (via the small connecting tube from the sump), it cannot compress and the sensor reports "low water" regardless of actual level. The board keeps filling.

Transducer failure: The electronic pressure transducer can drift with age. If it reports lower-than-actual pressure, the board overfills before reaching the threshold signal level.

Diagnosis: Enter diagnostic mode (Rinse + Spray for 3 seconds). During the fill test, observe the displayed water level value. If it does not increase even as water visibly rises in the tub, the pressure sensor system has failed.

3. Control Board Fill Circuit (15% of Cases)

The relay that controls the inlet valve solenoid can fail in the closed (stuck-on) position. This means the board continuously powers the valve even after receiving a "full" signal from the pressure sensor.

Rare but dangerous: This failure mode bypasses the software control completely. The base pan float switch becomes the only protection against overflow.

4. Drain Siphon / Backflow (10% of Cases)

Not technically an overflow from the fill system, but water entering the tub from the drain connection can simulate overfill:

LG installation requirement: The drain hose must have either an air gap or a high loop (rising above the flood rim level of the sink). Without this, dirty water from the sink or disposal can siphon backward into the dishwasher tub, raising the water level until FE triggers.

Diagnosis: Check if the "overflow" water is dirty or sudsy — backflow from the sink often contains food particles or soap from handwashing. Clean fill water from the inlet valve is clear.

5. Float Switch Failure (10% of Cases)

If the base pan float switch fails stuck in the "no water" position, the secondary overflow protection does not function. Combined with a primary sensor failure, this allows actual floor-level overflow.

Test: Remove the kick panel. Manually lift the polystyrene float — you should hear or feel the micro-switch click. If no click, the switch needs replacement. If the float does not move freely (stuck down by debris or mineral deposits), clean the float and its guide.

Immediate Response to an Overflowing LG Dishwasher

1. Turn off the water supply valve immediately (under the sink, behind the dishwasher, or at the main)
2. Power off the dishwasher at the circuit breaker
3. Remove standing water from the tub using a wet/dry vacuum or towels
4. Check for floor damage — lift flooring edges around the dishwasher if water reached the floor
5. Inspect the base pan — remove kick panel and dry the base pan to reset the float sensor
6. Do NOT simply restart the dishwasher — diagnose the overflow cause first

Repair Costs

Prevention

• Inspect the inlet valve mesh screen annually (10mm wrench to disconnect supply line)
• Verify drain hose high-loop installation is maintained (does not sag over time)
• Clean the sump area monthly during filter maintenance — prevents debris from entering the air trap
• Install a water leak sensor on the floor beneath the dishwasher for early overflow detection
• Run Smart Diagnosis through ThinQ app quarterly to check pressure sensor calibration

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