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Error code reference

LG Heat Pump Error Code E428

Outdoor unit compression rate 1 error (compression ratio over 8.5 for more than 5 minutes).

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What the E428 error code actually means

Your LG heat pump's outdoor unit is sensing that the compressor is working under extreme pressure stress and has been doing so for several minutes, so it shut down to protect itself. This is often caused by a refrigerant leak, a blocked valve, or a faulty component that controls how refrigerant flows through the system. A qualified technician should inspect and repair the unit before it is restarted, as continued operation in this condition can permanently damage the compressor.

Diagnostic procedure

The full E428 procedure

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1
First diagnostic step
Check service valves; check PWM valve coil and connector; check refrigerant.
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Most common causes of E428

Ranked by how often they cause this code
  1. 1Closed or partially closed service valves
  2. 2Low refrigerant charge due to a leak
  3. 3Faulty PWM expansion valve coil or connector
  4. 4Refrigerant overcharge
  5. 5Blocked or restricted refrigerant circuit

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Questions people ask about E428

What does E428 mean on a LG heat_pump?
E428 means the outdoor unit has detected a compression ratio above 8.5 for more than 5 consecutive minutes. The compression ratio is the discharge pressure divided by the suction pressure in the refrigerant circuit. When it stays that high for 5 minutes, the system shuts down to protect the compressor from damage. The most common causes include closed service valves, a refrigerant charge problem, or a malfunctioning PWM expansion valve.
Is it safe to keep running my heat pump when E428 appears?
No, you should not continue operating the unit after E428 triggers. An abnormally high compression ratio places severe mechanical and thermal stress on the compressor. Running the system in this condition risks permanent compressor failure, which is a much more costly repair than addressing the underlying cause early.
Will resetting my LG heat pump clear the E428 error?
A power reset may temporarily clear the fault and allow the unit to restart, but the error will return if the underlying cause is not corrected. Because E428 requires the high compression ratio to persist for more than 5 minutes before triggering, the system will fault again quickly if the pressure imbalance remains. Resetting without diagnosing and repairing the root cause is not a lasting solution and risks compressor damage.
Can I fix E428 on my LG heat pump myself?
Some steps, like checking that the outdoor unit service valves are fully open, can be done without special tools or certifications. However, diagnosing and correcting a refrigerant charge issue requires EPA Section 608 certification and manifold gauges, so that portion of the repair must be handled by a licensed HVAC technician. Inspecting and testing the PWM valve coil and connector is also a task best suited to someone with electrical diagnostic experience.
How much does it cost to repair an E428 error on an LG heat pump?
Repair costs vary widely depending on the root cause. Confirming and opening a closed service valve costs little beyond a service call fee, typically in the range of $75 to $150. Refrigerant leak detection, repair, and recharge can range from $200 to $600 or more depending on leak location and refrigerant type. Replacing a PWM expansion valve coil or the valve assembly itself generally falls in the $150 to $400 range for parts and labor.

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