Main controller communication failure (FTC receives nothing)
The FTC receives no data from the main remote controller for 3 minutes (E0 is the controller-side twin). Max 500 m 2-core cable, ONE main controller per FTC.
Safety: Safe isolation before opening terminal covers — mains present on the interconnect.
How to read it — ftc controller: Ecodan check codes show on the FTC / main controller display. (Ecodan service manual OCH727, §9-2 self-diagnosis action table)
UK models this code applies to
From the Mitsubishi Electric service literature we hold (Ecodan FTC service manual, error-code chapter + §10-6 thermistor tables) — not a scraped list.
E4 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.