Daikin U4

High

Altherma — Transmission malfunction indoor/outdoor unit.

Daikin U4: Transmission malfunction indoor/outdoor unit. This fault noticeably affects operation.

Possible causes

Short or wrong wiring F1/F2.
Outdoor unit off / address mismatch.

Check steps

Check F1/F2 for short.
Check power & addressing.

Affected parts

Verbindungsleitung F1/F2
Platine

Safety note

—

Source: Daikin resmi servis kılavuzu — Daikin Altherma HT ERSQ 011 AA Service Manual (ManualsLib p.220) and SM-TS3 chart: 'U4 — Malfunction of Transmission between Indoor Unit and Outdoor Unit' / 'Dysfonctionnement provoqué par la transmission entre les unités intérieure et extérieure' — detected when 'transmission is…

Reviewed by Anıl Güzeldemir — in the refrigeration machine room since 2006, developer of Enthalio.

Look up in Enthalio →

Related fault codes

Outdoor unit: PCB defect.E1 Power supply malfunction / brief power failureU2 Water flow malfunction – flow too low.7H Inverter compressor overload or overheat.E5 Abnormal discharge pipe temperature.F3 Plate heat exchanger freezing.89