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Quick answer
If an LG heat-pump water heater is not filling, leave its electrical power off and check the cold-water shut-off valve, inlet piping, and trapped air first. The tank must be completely full before power is restored. If the inlet is open but water still will not enter, or a connection leaks, stop and have a qualified installer inspect the supply and tank.
Before you begin
Safety first
- Do not energize a partly full tank or open electrical covers; repairs to wiring, controls, heating elements, and safety devices belong to qualified personnel.
Work through in order
Diagnostic checks
Use only checks that match the exact appliance or system and its official guide.
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Check 1
With the heater's electrical power left off, look at the cold-water shut-off valve and the cold-water pipe entering the unit. Confirm the valve is open and the pipe is not visibly crushed, frozen, or disconnected.
Expected result: The valve is closed or the inlet line is obstructed, or the valve and pipe look open and intact.
Next step: Open only the accessible shut-off valve fully. Do not energize the heater yet; if the line is damaged or frozen, arrange plumbing service.
Why this matters
Why: A closed or obstructed inlet can prevent the tank from filling; an open intact inlet means the restriction may be farther upstream or inside the installation.
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Check 2
At a nearby hot-water faucet, open the faucet while the cold-water supply is available and observe whether a steady stream eventually appears. Keep the faucet open only as a filling/air-release observation.
Expected result: Air spits and then water flows steadily, or no water arrives despite the inlet valve being open.
Next step: Once the stream is steady and the tank is full, close the faucet and follow the model start-up procedure. If no flow appears, stop and call a qualified service person.
Why this matters
Why: A steady stream indicates the tank and piping are filling and air is leaving; no flow points to a supply, connection, or installation problem rather than a heater control setting.
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Check 3
Inspect the floor, drain pan, hot and cold connections, and relief-valve discharge area while the supply is open. Look for a new drip or water accumulating outside the tank.
Expected result: The connections remain dry, or water is escaping from a fitting, drain, relief path, or the tank body.
Next step: Close the water supply if safe and do not turn on power. Never plug or cap a relief-valve outlet; have the plumbing and heater inspected.
Why this matters
Why: Dry connections support normal filling; an external leak can prevent safe commissioning and may indicate a loose connection, relief-pressure issue, or tank damage.
Use your observations
Decision map
Find the observation that best matches what you see, then follow the next safe action.
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PATH 01Next step
What you see
Water flows from the hot faucet after air clears and no external leak is present
Do this next
Close the faucet, verify the tank is full, and restore operation only according to the LG manual.
Why this path and its safety boundary
Why it matters: The tank is likely filled; the original symptom was an interrupted fill or trapped air rather than a proven electrical fault.
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PATH 02Next step
What you see
The inlet valve is open but no faucet flow develops
Do this next
Leave power off and request qualified plumbing/appliance service; do not remove covers to test valves.
Why this path and its safety boundary
Why it matters: The supply path, installation, or an internal restriction remains unresolved.
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PATH 03Next step
What you see
Water appears around a connection or the relief-valve discharge
Do this next
Shut off water if safe, keep the heater unpowered, and arrange qualified inspection.
Why this path and its safety boundary
Why it matters: This is a leak or pressure-safety symptom, not evidence that the tank merely needs more time to fill.
Helpful context
Understand the symptom
Do not heat an empty tank
A water heater that has just been drained or installed needs water and air removal before operation. The LG manual warns against energizing an empty or partly empty tank; a filling complaint is therefore a water-supply diagnosis first, not a heating-element test.
When checks do not resolve it
Need a professional?
Leave the heater unpowered for unresolved filling, leaking, or installation problems.
Safety scope: Do not energize a partly full tank or open electrical covers; repairs to wiring, controls, heating elements, and safety devices belong to qualified personnel.
Have this ready
- Provide the model, whether the cold valve is open, faucet-flow result, and the location of any water.
Common questions
FAQ
Can I turn on an LG water heater before it is full?
No. The LG manual says not to energize the heater unless the tank is completely full. Confirm water flow and remove air before restoring power.
What if the valve is open but the LG water heater still will not fill?
Keep power off. Check for a blocked or damaged supply path and have a qualified person inspect the installation rather than opening the heater cabinet.
Read the exact guide
Official sources
- MFL71409201-MN Owner's ManualLG Electronics · LG heat-pump water-heater filling, water connections, safety, and troubleshooting
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