Daikin U4 fault code
Daikin split air conditioning
What it means
Indoor/outdoor transmission error
Transmission between indoor and outdoor unit has failed (Daikin also lists outdoor power off and address mismatch).
Safety: Safe isolation before opening terminal covers — mains present on the interconnect.
How to read it — remote self-diagnosis, with beeps: Hold the remote's self-diagnosis button about 5 seconds until the code segment blinks, then press repeatedly to step through codes. A LONG CONTINUOUS beep from the indoor unit marks the stored code — a short or double beep means not this one. (Daikin CTXM/FTXM-M operation manual 3PEN393186-10J, remote self-diagnosis)
UK models this code applies to
From the Daikin service literature we hold (Daikin CTXM/FTXM-M operation manual 3PEN393186-10J, malfunction-code table (remote self-diagnosis)) — not a scraped list.
FTXM20R (RXM20A)FTXM25R (RXM25A)FTXM35R (RXM35A)FTXM42R (RXM42A)FTXM50R (RXM50A)FTXM60R (RXM60A)FTXM71R (RXM71A)MXM multi 2MXM40M2V1BMXM multi 2MXM50M2V1BMXM multi 3MXM40M2V1BMXM multi 3MXM52M2V1BMXM multi 3MXM68M2V1BMXM multi 4MXM68M2V1BMXM multi 4MXM80M2V1BMXM multi 5MXM90M2V1BRXS-L RXS20L2V1BRXS-L RXS25L2V1BRXS-L RXS35L2V1BRXS-L RXS42L2V1BRXS-L RXS50L2V1BRXS-L RXS60L2V1BComfora RXP20M5V1BComfora RXP25M5V1BComfora RXP35M5V1BComfora RXP50M2V1BComfora RXP60M2V1BComfora RXP71M2V1BSensira RXF20E5V1BSensira RXF25E5V1BSensira RXF35E5V1BSensira RXF42E5V1BSensira RXF50B2V1BSensira RXF60B2V1BSensira RXF71A2V1BStylish RXA20A2V1B — also badged FTXA20A2V1BS · FTXA20A2V1BTStylish RXA25A2V1B — also badged FTXA25A2V1BS · FTXA25A2V1BTStylish RXA35A2V1B — also badged FTXA35A2V1BS · FTXA35A2V1BTStylish RXA42A2V1B — also badged FTXA42A2V1BS · FTXA42A2V1BTStylish RXA50A2V1B — also badged FTXA50A2V1BS · FTXA50A2V1BTStylish RXA42B2V1B — also badged FTXA42A2V1BS · FTXA42A2V1BTStylish RXA50B2V1B — also badged FTXA50A2V1BS · FTXA50A2V1BTEmura RXJ50N2V1BEmura 2 RXJ20M2V1B — also badged FTXJ20MWEmura 2 RXJ25M2V1B — also badged FTXJ25MWEmura 2 RXJ35M2V1B — also badged FTXJ35MWEmura 2 RXJ50M2V1B — also badged FTXJ50MWEmura 3 RXJ20A5V1BEmura 3 RXJ25A5V1BEmura 3 RXJ35A5V1BEmura 3 RXJ42A2V1BEmura 3 RXJ50A2V1BDaikin Round flow cassette FCAG-A 3.5 kW (FCAG35A / RZAG35A2V1B)Daikin Round flow cassette FCAG-A 3.5 kW (FCAG50A / RZAG35A2V1B)Daikin Round flow cassette FCAG-A 5 kW (FCAG50A / RZAG50A2V1B)Daikin Round flow cassette FCAG-A 5 kW (FCAG60A / RZAG50A2V1B)Daikin Round flow cassette FCAG-A 6 kW (FCAG60A / RZAG60A2V1B)Daikin Round flow cassette FCAG-A 6 kW (FCAG71A / RZAG60A2V1B)Daikin Fully flat 600×600 cassette FFA-A9 3.4 kW (FFA35A9 / RXM35R9 · RZAG35A2V1B)Daikin Fully flat 600×600 cassette FFA-A9 3.5 kW (FFA50A9 / RZAG35A2V1B)Daikin Fully flat 600×600 cassette FFA-A9 5 kW (FFA50A9 / RZAG50A2V1B)Daikin Fully flat 600×600 cassette FFA-A9 5 kW (FFA60A9 / RZAG50A2V1B)Daikin Fully flat 600×600 cassette FFA-A9 6 kW (FFA60A9 / RZAG60A2V1B)Daikin Slim concealed duct FDXM-F9 3.4 kW (FDXM35F9 / RXM35R9 · RZAG35A2V1B)Daikin Slim concealed duct FDXM-F9 3.5 kW (FDXM50F9 / RZAG35A2V1B)Daikin Slim concealed duct FDXM-F9 5 kW (FDXM50F9 / RZAG50A2V1B)Daikin Slim concealed duct FDXM-F9 5 kW (FDXM60F9 / RZAG50A2V1B)Daikin Slim concealed duct FDXM-F9 6 kW (FDXM60F9 / RZAG60A2V1B)Daikin Medium static duct FBA-A9 3.5 kW (FBA35A9 / RXM35R9 · RZAG35A2V1B)Daikin Medium static duct FBA-A9 3.5 kW (FBA50A9 / RZAG35A2V1B)Daikin Medium static duct FBA-A9 5 kW (FBA50A9 / RZAG50A2V1B)Daikin Medium static duct FBA-A9 5 kW (FBA60A9 / RZAG50A2V1B)Daikin Medium static duct FBA-A9 6 kW (FBA60A9 / RZAG60A2V1B)Daikin Medium static duct FBA-A9 6 kW (FBA71A9 / RZAG60A2V1B)Daikin Ceiling suspended FHA-A9 3.4 kW (FHA35A9 / RXM35R9 · RZAG35A2V1B)Daikin Ceiling suspended FHA-A9 3.5 kW (FHA50A9 / RZAG35A2V1B)Daikin Ceiling suspended FHA-A9 5 kW (FHA50A9 / RZAG50A2V1B)Daikin Ceiling suspended FHA-A9 5 kW (FHA60A9 / RZAG50A2V1B)Daikin Ceiling suspended FHA-A9 6 kW (FHA60A9 / RZAG60A2V1B)Daikin Ceiling suspended FHA-A9 6 kW (FHA71A9 / RZAG60A2V1B)Daikin Concealed floor-standing FNA-A9 3.4 kW (FNA35A9 / RXM35R9 · RZAG35A2V1B)Daikin Concealed floor-standing FNA-A9 3.5 kW (FNA50A9 / RZAG35A2V1B)Daikin Concealed floor-standing FNA-A9 5 kW (FNA50A9 / RZAG50A2V1B)Daikin Concealed floor-standing FNA-A9 5 kW (FNA60A9 / RZAG50A2V1B)Daikin Concealed floor-standing FNA-A9 6 kW (FNA60A9 / RZAG60A2V1B)Daikin Round flow cassette FCAG-B 3.4 kW (FCAG35B / RXM35R9 · RZAG35A)Daikin Slim concealed duct FDXM-F9 2.4 kW (FDXM25F9 / RXM25R9)Daikin Fully flat 600×600 cassette FFA-A9 2.5 kW (FFA25A9 / RXM25R9)Daikin Concealed floor-standing FNA-A9 2.6 kW (FNA25A9 / RXM25R9)Daikin Perfera floor FVXM-A 2.4 kW (FVXM25A / RXM25R9)Daikin Perfera floor FVXM-A 3.4 kW (FVXM35A / RXM35R9)Daikin Perfera floor FVXM-A 5 kW (FVXM50A / RXM50R)Daikin Round flow cassette FCAG-B 5 kW (FCAG50B / RZAG50A)Daikin Round flow cassette FCAG-B 5.7 kW (FCAG60B / RZAG60A)Daikin Wall FTXS-K 2 kW (FTXS20K / RXS20L2V1B)Daikin Wall FTXS-K 2.5 kW (FTXS25K / RXS25L2V1B)Daikin Wall FTXS-K 3.5 kW (FTXS35K / RXS35L2V1B)Daikin Wall FTXS-K 4.2 kW (FTXS42K / RXS42L2V1B)Daikin Wall FTXS-K 5 kW (FTXS50K / RXS50L2V1B)Daikin Wall FTXS-G 6 kW (FTXS60G / RXS60L2V1B)Daikin Floor console FVXS-F 2.5 kW (FVXS25F / RXS25L2V1B)Daikin Floor console FVXS-F 3.5 kW (FVXS35F / RXS35L2V1B)Daikin Floor console FVXS-F 5 kW (FVXS50F / RXS50L2V1B)Daikin Flexi floor/ceiling FLXS-B 2.5 kW (FLXS25B / RXS25L2V1B)Daikin Flexi floor/ceiling FLXS-B 4.9 kW (FLXS50B / RXS50L2V1B)Daikin Flexi floor/ceiling FLXS-B 3.5 kW (FLXS35B9 / RXS35L2V1B)Daikin Slim duct FDXS-F 2.4 kW (FDXS25F / RXS25L2V1B)Daikin Slim duct FDXS-F 3.4 kW (FDXS35F / RXS35L2V1B)Daikin Slim duct FDXS-F 6 kW (FDXS60F / RXS60L2V1B)Daikin Slim duct FDXS-F 5 kW (FDXS50F9 / RXS50L2V1B)Daikin Round flow cassette FCQG-F 3.4 kW (FCQG35F / RXS35L2V1B)Daikin Round flow cassette FCQG-F 5 kW (FCQG50F / RXS50L2V1B)Daikin Round flow cassette FCQG-F 5.7 kW (FCQG60F / RXS60L2V1B)Daikin Fully flat cassette FFQ-C 2.5 kW (FFQ25C / RXS25L2V1B)Daikin Fully flat cassette FFQ-C 3.4 kW (FFQ35C / RXS35L2V1B)Daikin Fully flat cassette FFQ-C 5 kW (FFQ50C / RXS50L2V1B)Daikin Fully flat cassette FFQ-C 5.7 kW (FFQ60C / RXS60L2V1B)Daikin Medium static duct FBQ-C 3.4 kW (FBQ35C8 / RXS35L2V1B)Daikin Medium static duct FBQ-C 5 kW (FBQ50C8 / RXS50L2V1B)Daikin Medium static duct FBQ-C 5.7 kW (FBQ60C8 / RXS60L2V1B)Daikin Ceiling suspended FHQ-C 3.4 kW (FHQ35C / RXS35L2V1B)Daikin Ceiling suspended FHQ-C 5 kW (FHQ50C / RXS50L2V1B)Daikin Ceiling suspended FHQ-C 5.7 kW (FHQ60C / RXS60L2V1B)Daikin Round flow cassette FCAG-A 6.8 kW (FCAG71AVEB / RZASG71M2V1B)Daikin Round flow cassette FCAG-A 9.5 kW (FCAG100AVEB / RZASG100M7V1B)Daikin Round flow cassette FCAG-A 12.1 kW (FCAG125AVEB / RZASG125M7V1B)Daikin Round flow cassette FCAG-A 13.4 kW (FCAG140AVEB / RZASG140M7V1B)Daikin Medium static duct FBA-A2 6.8 kW (FBA71A2VEB / RZASG71M2V1B)Daikin Medium static duct FBA-A2 9.5 kW (FBA100A2VEB / RZASG100M7V1B · RZASG100M7Y1B)Daikin Medium static duct FBA-A2 12.1 kW (FBA125A2VEB / RZASG125M7V1B · RZASG125M7Y1B)Daikin Medium static duct FBA-A2 13.4 kW (FBA140A2VEB / RZASG140M7V1B · RZASG140M7Y1B)Daikin Ceiling suspended FHA-A 6.8 kW (FHA71AVEB / RZASG71M2V1B)Daikin Ceiling suspended FHA-A 9.5 kW (FHA100AVEB / RZASG100M7V1B · RZASG100M7Y1B)Daikin Ceiling suspended FHA-A 12.1 kW (FHA125AVEB / RZASG125M7V1B · RZASG125M7Y1B)Daikin Ceiling suspended FHA-A 13.4 kW (FHA140AVEB / RZASG140M7V1B · RZASG140M7Y1B)Daikin 4-way blow ceiling suspended FUA-A 6.8 kW (FUA71AVEB / RZASG71M2V1B)Daikin 4-way blow ceiling suspended FUA-A 9.5 kW (FUA100AVEB / RZASG100M7V1B · RZASG100M7Y1B)Daikin 4-way blow ceiling suspended FUA-A 12.1 kW (FUA125AVEB / RZASG125M7V1B · RZASG125M7Y1B)Daikin Wall FAA-A 6.8 kW (FAA71AUVEB / RZASG71M2V1B)Daikin Wall FAA-A 9.5 kW (FAA100AUVEB / RZASG100M7V1B · RZASG100M7Y1B)Daikin Floor standing FVA-A 6.8 kW (FVA71AMVEB / RZASG71M2V1B)Daikin Floor standing FVA-A 9.5 kW (FVA100AMVEB / RZASG100M7V1B · RZASG100M7Y1B)Daikin Floor standing FVA-A 12.1 kW (FVA125AMVEB / RZASG125M7Y1B)Daikin Floor standing FVA-A 13.4 kW (FVA140AMVEB / RZASG140M7V1B · RZASG140M7Y1B)Daikin Round flow cassette FCAHG-G 6.8 kW (FCAHG100GVEB / RZAG71M7V1B · RZAG71M7Y1B)Daikin Round flow cassette FCAHG-G 9.5 kW (FCAHG100GVEB / RZAG100M7V1B · RZAG100M7Y1B)Daikin Round flow cassette FCAHG-G 6.8 kW (FCAHG71GVEB / RZAG71M7V1B · RZAG71M7Y1B)Daikin Round flow cassette FCAHG-G 9.5 kW (FCAHG140GVEB / RZAG100M7V1B · RZAG100M7Y1B)Daikin Round flow cassette FCAHG-G 13.4 kW (FCAHG140GVEB / RZAG140M7V1B · RZAG140M7Y1B)Daikin Round flow cassette FCAHG-G 12.1 kW (FCAHG125GVEB / RZAG125M7V1B · RZAG125M7Y1B)Daikin Round flow cassette FCAHG-G 6.8 kW (FCAHG71H / RZAG71NV1 · RZAG71NY1)Daikin Round flow cassette FCAHG-G 6.8 kW (FCAHG100H / RZAG71NV1 · RZAG71NY1)Daikin Round flow cassette FCAHG-G 9.5 kW (FCAHG100H / RZAG100NV1 · RZAG100NY1)Daikin Round flow cassette FCAHG-G 9.5 kW (FCAHG140H / RZAG100NV1 · RZAG100NY1)Daikin Round flow cassette FCAHG-G 13.4 kW (FCAHG140H / RZAG140NV1 · RZAG140NY1)Daikin Round flow cassette FCAHG-G 12.1 kW (FCAHG125H / RZAG125NV1 · RZAG125NY1)Daikin High static duct FDA-A 12.1 kW (FDA125A5VEB / RZAG125M7Y1B)Daikin Large duct FDQ-B 20 kW (FDQ200B / RZQ200C)Daikin Large duct FDQ-B 24.1 kW (FDQ250B / RZQ250C)Daikin High static duct FDA-A 12 kW (FDA125A / RZAG125NV1 · RZAG125NY1 · RZQG125L9V1 · RZQG125L8Y1 · RZQSG125L9V1 · RZQSG125L8Y1)RXM71MRXF50D6V1BFTXF20F5V1B / RXF20F5V1BFTXF25F5V1B / RXF25F5V1BFTXF35F5V1B / RXF35F5V1BFTXF42F5V1B / RXF42F5V1BFTXF50F5V1B / RXF50F5V1BFTXF60F2V1B / RXF60D5V1B9FTXF71F2V1B / RXF71D5V1B9RXP60N5V1B9RXP71N5V1B9FTXP20N5V1B / RXP20N5V1BFTXP25N5V1B / RXP25N5V1BFTXP35N5V1B / RXP35N5V1BFTXP50N2V1B / RXP50N5V1BFTXP60N2V1B / RXP60N5V1BFTXP71N2V1B / RXP71N5V1BFTXP20N5V1B9 / RXP20N5V1B9FTXP25N5V1B9 / RXP25N5V1B9FTXP35N5V1B9 / RXP35N5V1B9FTXP50N5V1B9 / RXP50N5V1B9FTXM20A / RXM20A5V1BFTXM25A / RXM25A5V1BFTXM35A / RXM35A5V1BFTXM42A / RXM42A5V1BFTXM50A / RXM50A5V1BFTXM60A2V1B / RXM60A5V1BFTXM71A2V1B / RXM71A5V1BCTXM15ARXM25A5V1B9RXM35A5V1B9RXM50A5V1B8RXP50N5V1B8RXM50A5V1B9FTXA20C2V1BW / RXA20A9FTXA25C2V1BW / RXA25A9FTXA35C2V1BW / RXA35A9FTXA42C2V1BW / RXA42B9FTXA50C2V1BW / RXA50BFTXA20C2V1BB / RXA20A9FTXA25C2V1BB / RXA25A9FTXA35C2V1BB / RXA35A9FTXA42C2V1BB / RXA42B9FTXA50C2V1BB / RXA50BFTXA20C2V1BS / RXA20A9FTXA25C2V1BS / RXA25A9FTXA35C2V1BS / RXA35A9FTXA42C2V1BS / RXA42B9FTXA50C2V1BS / RXA50BFTXA20B2V1BB / RXA20A9FTXA25B2V1BB / RXA25A9FTXA35B2V1BB / RXA35A9FTXA42B2V1BB / RXA42B9FTXA50B2V1BB / RXA50BFTXA20B2V1BS / RXA20A9FTXA25B2V1BS / RXA25A9FTXA35B2V1BS / RXA35A9FTXA42B2V1BS / RXA42B9FTXA50B2V1BS / RXA50BFTXA20B2V1BT / RXA20A9FTXA25B2V1BT / RXA25A9FTXA35B2V1BT / RXA35A9FTXA42B2V1BT / RXA42B9FTXA50B2V1BT / RXA50BRXA42B5V1B9RXA50B5V1BFTXJ20A2V1BW / RXJ20AFTXJ25A2V1BW / RXJ25AFTXJ35A2V1BW / RXJ35AFTXJ42A2V1BW / RXJ42AFTXJ50A2V1BW / RXJ50AFTXJ20A2V1BS / RXJ20AFTXJ25A2V1BS / RXJ25AFTXJ35A2V1BS / RXJ35AFTXJ42A2V1BS / RXJ42AFTXJ50A2V1BS / RXJ50AFTXJ20A2V1BB / RXJ20AFTXJ25A2V1BB / RXJ25AFTXJ35A2V1BB / RXJ35AFTXJ42A2V1BB / RXJ42AFTXJ50A2V1BB / RXJ50ARXZ25NV1B9FTXZ25NV1B / RXZ25NV1BRXZ35NV1B9FTXZ35NV1B / RXZ35NV1BRXZ50NV1B9FTXZ50NV1B / RXZ50NV1B2MXM40A2V1B2MXM50A2V1B2MXM68A2V1B3MXM40A2V1B3MXM52A2V1B3MXM68A2V1B4MXM68A2V1B4MXM80A2V1B5MXM90A2V1B4MWXM52A2V1B5XXM68A2V1B5XXM90A2V1B2MXF40B2V1B2MXF50B2V1B3MXF52B2V1B3MXF68B2V1BRZA200D7Y1BRZA250D7Y1BRZAG35B5V1BRZAG50B5V1BRZAG60B5V1B
Now the harder half: proving what caused it
U4 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.
Chase U4 on your machine →Free, no sign-up. Pick the model and follow Daikin's own chart for it, one question at a time.
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