All four rooms went warm: single leak at the outdoor unit

All four rooms went warm within days of each other. When every room on a system 4 fades together, the fault usually sits in the one part they all share: the outdoor unit. The question was whether it could be repaired or had to be replaced.

By Team Snowflake | Updated 28 Jul 2026

Case summary

LG Multi-split5 years oldHDBSengkang, Singapore

Concern: The homeowner feared each room had its own fault, which would mean several separate repair bills.
Found: Gas leak at outdoor unit pipe connections on shared system 4 outdoor unit, causing cooling loss across all rooms
Key check: Checking gas pressure confirmed system-wide gas loss. Then bubble test at outdoor connections pinpointed the leak source
Result: We replaced the full system: a new outdoor unit and four new indoor units. The piping was pressure-tested for leaks before charging, and the refrigerant was set to the correct level. Cooling returned to all four rooms, with no further gas loss on follow-up.

What we were told

The master bedroom lost cooling first. The other three rooms followed over the next few days, until all four were blowing warm air. The homeowner assumed each room had its own separate fault. The system was about five years old.

What we checked

Separate faults rarely show up in four rooms within the same week. The one part all four share is the outdoor unit, so we checked it first before opening up any indoor unit.

Gas pressure read very low across the whole system, not just one room.
All four indoor units pushed air but none of it was cold, which fits a system-wide gas loss.
The outdoor unit pipe manifold, where every room's line connects, showed corrosion and oxidation on several joints.
A bubble test on those joints found active leaks at two connection points.
LG error code CH38 was showing on the system controller.

What we found

The outdoor unit had developed gas leaks at the pipe manifold where all four indoor lines connect. Corrosion had spread across several joints. A system 4 runs every room off one shared refrigerant circuit, so a leak here drains all four rooms at once. The master bedroom faded first because its line is the longest, so it felt the drop in pressure before the others did.

What fixed it

Welding several corroded joints on one manifold is risky. If any single weld fails later, all four rooms lose cooling again. With corrosion across multiple joints, and the indoor units already showing their age, a patch repair was the weaker option. We walked through replacing the outdoor unit alone, but the worn indoor units would likely fail next, so a full change was the more reliable path. The homeowner approved full system replacement.

Outcome

We replaced the full system: a new outdoor unit and four new indoor units. The piping was pressure-tested for leaks before charging, and the refrigerant was set to the correct level. Cooling returned to all four rooms, with no further gas loss on follow-up.

What this case teaches us

When every room fails together, check the shared outdoor unit first

On a system 4, all four rooms run off one outdoor unit. If they all go warm in close succession, suspect that shared part before any single room.
A gas leak at the outdoor pipe joints starves every room at once. The room with the longest pipe run tends to fade first.
Before approving a weld repair on a corroded manifold, ask how many joints are affected. Several failing joints often mean replacement is the safer call.

Questions this case answers

All rooms on a System 4 went warm within days: are there four separate faults?

Almost certainly one. Four rooms rarely develop separate faults in the same week, and on a System 4 every room runs off one shared refrigerant circuit. Gas pressure read very low across the whole system here, and all four indoor units pushed air that was not cold.

Why did one room lose cooling before the others?

The longest line feels a pressure drop first. In this Sengkang flat the master bedroom faded ahead of the rest for that reason, with the other three following over the days after. The ordering is a clue in itself, because it points at a shared circuit losing charge rather than a local fault.

When is welding a leaking manifold the wrong call?

When corrosion has spread across several joints rather than sitting at one. The manifold here carried oxidation on several connections and a bubble test found active leaks at two of them. If any single weld later gives way, every room loses cooling again. Ask how many joints are affected before approving a patch.

Why replace the whole system instead of welding the leaks?

Because the alternative was a patch on a manifold corroded across it, on a set whose indoor units were already showing their age. Replacing only the outdoor unit would have left those indoor units next in line. Both paths were walked through before the full change was approved, and new piping was pressure-tested before charging.

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