Error code
04 Serial signal or connecting cable fault
How it shows on the unit Shown on the remote control display in service-check mode (CHECK button); all indoor-unit lamps flash 5 times per second
Applies to 4 models
RAS-25G2KVP-ND, RAS-35G2KVP-ND, RAS-25G2AVP-ND, RAS-35G2AVP-ND
What this means
No working signal between the indoor and outdoor units (for example a connecting-cable fault). The indoor unit keeps running but the outdoor unit stops.
When to call a technician
This fault involves refrigerant, pressure, or electrical work that must be handled by a certified technician under EU F-gas rules. Do not attempt to open the refrigerant circuit, access mains wiring, or adjust pressure components yourself. Contact a qualified installer or servicer for this one.
Using Claude Code or Meta Muse? Connect HeatPump AI and ask it about 04.