Random Error Code With No Pattern: Drain Pump Cable Causing Interference

• •Concern: Worry was that the indoor PCB was developing an intermittent fault and would need replacement
• •Key check: E6 timing correlated exactly with drain pump activation cycles. Separating cables eliminated the error

An intermittent communication error with no correlation to cooling load or run time suggests an external interference source rather than an internal fault. We checked the cable routing inside the ceiling void.

• •E6 error code logged. Indoor-outdoor communication fault.
• •Terminal connections at both indoor and outdoor units were clean and secure.
• •Wiring continuity checked normal end to end.
• •Communication cable was routed alongside the condensate drain pump power cable inside the ceiling void, running parallel for about 2 metres.
• •E6 timing correlated exactly with drain pump activation. The error appeared within seconds of the pump switching on and cleared shortly after it stopped.

The communication cable had been routed alongside the drain pump power cable during the original installation. Both ran parallel for about 2 metres inside the ceiling void. When the pump motor activated, it generated interference strong enough to disrupt the low-voltage signal. The pump runs on a float switch tied to water level, not cooling demand. That is why the error appeared random. The PCB, wiring, and pump were all healthy. The fault was purely a routing issue.

We separated the communication cable from the pump power cable, creating about 30cm of clearance inside the void. We also fitted a ferrite core on the signal cable near the indoor unit to suppress residual noise. After rerouting, we ran the unit through multiple pump cycles while monitoring for E6. No errors appeared.

The E6 error stopped completely after separating the cables and adding the ferrite core. The unit has been running without communication faults since. No PCB, wiring, or pump components were replaced.

Electromagnetic interference from drain pumps on communication signals.

• •Condensate drain pump motors generate electromagnetic noise when they switch on and off. If the signal cable runs alongside the pump power cable, that noise can corrupt the communication signal.
• •The key diagnostic clue is timing. If E6 appears at irregular intervals unrelated to cooling load, check whether a drain pump is installed. Then check if pump activation coincides with the error. The pump runs on a float switch tied to condensate volume, not cooling demand.
• •Separating the cables by at least 30cm and adding a ferrite core on the signal cable are standard fixes. No parts need replacing. The PCB, wiring, and pump all function correctly on their own.