LG Refrigerator Not Defrosting: Causes & Fix
When an LG refrigerator stops defrosting, the most likely cause — around 35% of cases — is a failed defrost heater that no longer melts the frost off the evaporator coil. The defrost thermostat, the main-board defrost relay, the drain heater, and a drifting evaporator thermistor account for the rest.
Frost Buildup Points to the Defrost Circuit#
Every frost-free LG runs a defrost cycle: several times a day the compressor pauses and a heater warms the evaporator coil just enough to melt accumulated frost, which drains away. When one part of that circuit fails, frost keeps building on the coil, airflow through it chokes, and the fridge slowly loses its ability to cool even though the compressor runs.
Ranked Causes on LG Refrigerators#
| What you notice | Likely cause | Share of cases | Fix path |
|---|---|---|---|
| Thick frost on the evaporator; fridge warming despite runtime | Defrost heater failure | 35% | Replace the defrost heater |
| Frost returns days after a manual defrost | Defrost thermostat (bi-metal) failure | 25% | Replace the bi-metal thermostat |
| Coil frosts, heater tests good | Main board defrost relay failure | 20% | Replace the main control board |
| Water pooling or ice under the drawers | Defrost drain heater failure | 12% | Clear and replace the drain heater |
| Temperatures wander with light frost | Evaporator thermistor drift | 8% | Replace the evaporator thermistor |
The defrost heater leads because it does the physical work and carries the most stress. When it opens, nothing melts the frost, and the coil ices over solid. The bi-metal thermostat is next — it has to close to let the heater run, and a failed one starves the heater of power even when the heater itself is fine.
If both test good, the main-board relay that switches the defrost circuit may not be firing, which mimics a dead heater. A separate drain heater keeps the defrost water channel clear; when it fails you get ice and water under the drawers rather than a warm box. And a drifting thermistor can confuse the control into skipping or shortening defrosts.
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Refrigerant gauges ($200+), vacuum pump ($250), leak detector ($150), and EPA-certified recovery equipment. Our technician arrives with $3,000+ in professional tools — your diagnostic is free.
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What You Can Check Safely#
The clearest home test is a manual defrost. Empty the fridge and freezer, unplug it, and let it sit open for a day so all the frost melts. Plug it back in: if it cools normally for two or three days and then warms again as frost rebuilds, the defrost circuit is confirmed as the fault — cooling itself is fine, but nothing is clearing the coil. That single observation separates a defrost problem from a sealed-system or compressor problem.
While it's open, look at where the frost and water collect. Heavy frost on the coil points at the heater or thermostat; water or ice under the drawers points at the drain heater. Beyond a manual defrost and a visual check, testing the heater, thermostat, and 120-volt board circuit means reaching the evaporator behind the freezer panel with the power isolated — a job for a technician.
Why a Defrost Fault Slowly Kills Cooling#
It helps to understand why a stalled defrost cycle looks so much like a dying refrigerator, because the two are easy to confuse. The evaporator coil is where cold is produced, and air is pulled across it and pushed into the compartments. When defrost stops working, frost keeps accumulating on that coil layer after layer until it becomes a solid block of ice. That ice insulates the coil and blocks the airflow path, so even though the compressor runs constantly and the coil is bitterly cold, almost no cold air reaches the food. The result is a fridge that warms up while running non-stop — which many owners misread as a failing compressor. The tell is the timeline: a defrost fault cools fine right after a manual defrost and only degrades over the following days as frost rebuilds, whereas a sealed-system failure never recovers even after the coil is cleared. That distinction is exactly what a manual defrost test reveals.
Safety First — Know the Risks
Refrigerant (R-134a/R-600a) requires EPA certification to handle. Improper discharge is a federal violation and health hazard. Our techs are licensed and insured — let them handle the risk.
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Getting It Fixed#
Most no-defrost calls end with a new heater or thermostat once the part is confirmed. Book a diagnostic and we'll test the defrost heater, thermostat, and board so the right part goes in the first time.
Senior Appliance Repair Technician · 15 years experience
EPA-certified technician with 15 years of experience specializing in refrigerator and cooling system repairs.
