If your LG refrigerator shows gF or 9F, it’s trying to tell you there’s a problem with the water supply to the ice/water system. Most commonly this points to low water pressure or a faulty flow sensor (the part that measures how much water goes to the ice maker). Below is a clear, easy-to-read guide that explains the fault, walks you through safe DIY checks and fixes, and gives practical preventive steps so the code is less likely to come back.

Quick plain-language summary

Your fridge needs a reliable, properly pressured water feed for the ice maker and dispenser. If pressure is too low (below ~20 psi) or the flow sensor is giving bad readings, the fridge will show gF / 9F and suspend ice/water functions to avoid overfilling or poor operation.

Common signs you have this problem

• The refrigerator displays gF or 9F.
• Ice maker is slow to fill or makes little/no ice.
• Ice maker overfills and water spills into the ice bin.
• Water dispenser flow is weak or inconsistent.

Typical causes

The two most frequent causes are:

• Low incoming water pressure (too weak to properly feed the ice maker).
• Faulty flow sensor in the water line (it can fail or give incorrect readings, which may cause overfilling or the error code).

Other possible but less common causes include a clogged water filter, a kinked or frozen supply line, or a bad water inlet valve.

Basic safety and tools

Before you start, unplug the fridge or shut off power at the breaker if you’ll be disconnecting plumbing or working near electrical components. Wait until any ice-making cycle finishes and the area is dry.

Tools you might need:

• Pressure gauge for water lines (quick-connect type), or an inline gauge.
• Multimeter (to test sensor continuity, if applicable).
• Basic hand tools: adjustable wrench, screwdrivers, needle-nose pliers.
• Replacement flow sensor (model-specific) and new water filter if needed.

Step-by-step DIY diagnostic

1. Check the refrigerator’s water filter. A clogged filter reduces pressure. Replace it if it’s old or blocked.
2. Inspect the water supply line behind the fridge. Make sure it isn’t kinked, pinched, or frozen. Straighten or thaw as needed.
3. Measure incoming water pressure at the cold-water supply for the fridge. If you don’t have a gauge, run a hose bib on the same feed and judge flow — very weak flow suggests low pressure.
4. If pressure is below 20 psi, increase water pressure or call the building/plumbing service — most refrigerators work best between 40–120 psi.
5. If pressure is adequate but the ice maker is overfilling or code persists, test the flow sensor and its wiring.

How to test the flow sensor

• Locate the flow sensor: it’s usually on the water line to the ice maker or behind the control panel. Consult your model’s manual or photos online if unsure.
• Visually inspect the sensor and connector for corrosion, loose pins, or water damage.
• If you have a multimeter, check continuity according to the sensor’s spec (if you don’t have the spec, you can still check for open-circuit — a totally open sensor usually means failure).
• If readings are out of range, the sensor should be replaced.

Replacing the flow sensor

Replacing the sensor is often straightforward:

• Turn off water and power.
• Disconnect the water line at the sensor (prepare a towel for spills).
• Unplug the electrical connector and remove mounting screws.
• Install the new sensor, reconnect wiring and water line, restore water and power, then run a test cycle.

After replacement, watch the first few fill cycles to confirm the ice maker fills normally and the gF / 9F code is gone.

What if the water pressure is the problem

Low pressure can come from:

• Closed or partially closed shutoff valve behind the fridge.
• Building plumbing problems (low municipal pressure or pressure-reducing valve set too low).
• A clogged supply line or filter.

If your home pressure is below ~20 psi, contact a plumber or building maintenance. Increasing pressure often fixes the issue; refrigerators prefer the 40–120 psi range for reliable ice/water operation.

When to call a professional

• You find corrosion or damage inside the fridge electronics or control board area.
• The fridge still shows gF / 9F after replacing the sensor and verifying adequate water pressure.
• You’re uncomfortable turning off water or working with the supply plumbing.
• The inlet valve or control module appears to be failing (these can require parts and diagnostic tools).

A pro can test inlet valve function, measure exact flow rates, and check the control logic that interprets the flow sensor.

Preventive tips

• Replace the water filter on schedule — a clogged filter reduces flow and stresses sensors.
• Keep the supply line free of kinks and insulated in cold spaces to avoid freezing.
• When moving the fridge, take care not to bend or pinch the water line or wiring.
• If your home has hard water or sediment, consider a whole-house pre-filter to protect refrigerator components.

Regular filter changes and simple visual checks of the supply line go a long way toward avoiding gF / 9F issues.

Quick troubleshooting checklist

• Replace the water filter if it’s old or clogged.
• Ensure the water shutoff valve is fully open and the line isn’t kinked.
• Measure or evaluate house water pressure — below ~20 psi is problematic.
• If pressure is low, address plumbing or pressure-regulator settings.
• If pressure is OK but code continues, test and likely replace the flow sensor.
• Call a professional if the inlet valve, wiring, or control board appears to be the cause.

Final notes

Most gF / 9F problems come down to water pressure or the flow sensor — both are fixable at home if you’re comfortable with simple plumbing and a multimeter. Start with the easiest items (filter, kinked line, shutoff valve), then move to pressure checks and sensor testing.