One unit showing error, others fine: indoor board dead
E1 showed on one bedroom unit while the other two in the system ran fine. A whole-system fault would hit all three, so the problem sat in that one unit's wiring or its indoor board. The job was to prove which, before quoting any part.
By Team Snowflake | Reviewed 24 Mar 2026
Case summary
Samsung Wall-mounted10 years oldCondoSengkang, Singapore
- Concern
- The owner worried the outdoor unit or the whole system wiring had failed
- Found
- Indoor unit control board communication relay failure
- Key check
- control board swap test. E1 followed the board to the second room, confirming indoor control board fault
- Result
- We installed the replacement bedroom control board and E1 cleared straight away. All three units now run normally. The swap test took the guesswork out of the diagnosis, so the owner paid for one board and nothing more.
What we were told
One of three aircon units had shown an error code for about a week while the other two worked fine. The owner wanted to know whether it was a wiring problem or a fault inside the unit, and how much it would cost to fix.
What we checked
One unit faulting while the other two ran normally pointed to a fault inside that single indoor unit. The shared outdoor unit and the system wiring would affect all three if they were the cause, so we checked the local wiring first, then tested the board.
E1 stayed on the bedroom unit the whole time, and the unit would not start.
The other two indoor units ran normally with no errors, which ruled out a shared system fault.
The communication cable between the bedroom unit and the outdoor unit tested intact, with correct continuity end to end.
Wire connections at both ends were clean, with no corrosion to break the signal.
With wiring cleared, we swapped the bedroom control board into the living room unit. E1 followed the board to the living room, and the bedroom unit then ran fine on the living room board.
What we found
The communication relay on the bedroom indoor control board had failed. That relay carries the signal between the indoor board and the outdoor unit. Once it fails, the unit can no longer talk to the outdoor unit, and the system throws E1. The swap test settled it: the fault travelled with the board to the living room, while the bedroom unit ran fine on a working board. The wiring was sound, so the board was the only part left to blame.
What fixed it
We recommended replacing only the bedroom unit control board. The wiring, the outdoor unit, and the other two indoor units were all confirmed working, so there was nothing else to fix. We sourced the correct board for the model. At seven-plus years, the other boards may fail in time, but we do not replace parts that still work normally. The owner can address them if and when they fault.
Outcome
We installed the replacement bedroom control board and E1 cleared straight away. All three units now run normally. The swap test took the guesswork out of the diagnosis, so the owner paid for one board and nothing more.
What this case teaches us
One unit faulting in a multi-split points to that unit
- When one unit errors and the others run fine, the fault is local to that unit, not the shared outdoor unit or system wiring.
- A swap test isolates a board fault cheaply. If the error follows the board to another room, the board is the problem, not the wiring.
- Confirm the part before ordering it. A E1 board swap takes a few minutes and rules out a wasted parts cost.
Related reading
Ready to get started?
Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.