All Four Rooms Down at Once: Outdoor Board Died

All four rooms go down at once and damaged wiring is suspected. Whether the walls need opening or the fault sits in one place.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

How this presents

A lost-communication code, with the outdoor unit powering up, running its fan and responding to its own controls. Only the link between the two units has stopped working. Cabling has been checked along its length and is sound.

Setup: LG Multi-split10-12 yearsCondoTampines
Misread as: Damaged wiring somewhere in the property, needing walls opened to find and repair it.
Check first: Whether the unit still performs every function except the one that has stopped

What else produces this

An outdoor unit doing everything except communicating is a specific and useful observation, because it eliminates power, supply and most of the board at once. What remains is the part of the board handling the link, and a partial failure there is entirely possible. The board is not dead and does not behave as though it is, which is exactly why the search keeps returning to the cabling instead.

An outdoor unit powering up and running its fan proves supply and most of the board are working.
Cabling checked sound along its length removes the run between the units from consideration.
A signal arriving at the board with no reply leaving it isolates the failure to one circuit.
Every other board function operating normally shows the failure is partial rather than total.

Why it happens

Any board of this kind holds several separate circuits sharing one piece of hardware. A surge, a component failure or moisture can take out the section handling communication and leave the rest untouched. The unit continues to power up, drive its fan and respond to local controls, so nothing about its behaviour suggests a board at all. Only the missing function does, and that function is invisible until somebody measures it.

What resolution involves

The board is replaced once the one dead circuit has been demonstrated rather than assumed. The reasoning is what carries: a board is not a single thing that works or does not, so a system behaving normally in every other respect is not evidence that its board is healthy. Test the function that is missing, not the ones that are present.

How to tell it worked

Several days of watching the link after the change, since the original fault was total rather than intermittent. A restored link that stays restored is what proves the diagnosis was right.

Before you approve a quote

A board can lose one circuit and keep the rest

Boards hold separate circuits. One can fail while every other function carries on normally.
A unit that powers up and runs its fan has proved its supply, not its communication circuit.
Test the function that is missing. The functions still working say nothing about the one that is not.

Questions this case answers

All four aircon units showing the same error at once: is the whole system finished?

Usually not. It is one shared part rather than the whole system. A board is several circuits on one piece of hardware, and they do not all fail together: one section can stop while the rest continue driving the fan, responding to controls and powering up normally.

Can one failed circuit stop every room in a multi-split?

Yes, when the failed circuit is the one every room depends on. A unit that powers up and runs proves only that much of the board is working; it says nothing about the specific circuit that has stopped, which is why a healthy-looking unit can still have a board fault.

What separates a wiring fault from a board fault on a multi-split?

A signal test at the outdoor connection point is what separates them. Everything visible can work. The unit powers up and the fan runs, yet the only thing missing is a signal nobody can see, so wiring stays the natural suspect even after it has been checked.

Should the indoor units be replaced at the same time as the outdoor board?

No, not unless they have failed their own checks. Demonstrate that a signal reaches the board correctly and nothing appropriate leaves it; that combination isolates the failure to the board itself rather than to anything before or after it, so nothing sound gets swapped.

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Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.

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