If none of those is on the screen, the codes below tell you what Daikin itself says to do next. Most of them allow one careful check and one reset, and no more.
First: the three things that pause heat on purpose
- DEFROST. Let it finish. Daikin's guidance is to keep snow from building up around the base of the outdoor unit, and not to chip ice off the coil. Frequent back-to-back defrosts with little heat in between are a different story. That belongs in the call-a-technician list below. For how the cycle works, see the defrost cycle explained.
- 3-minute standby. Wait several minutes without pressing buttons or cycling the breaker. Operation resumes when the protection timer ends.
- Mode conflict. Set every head on the system to the same mode, then wait a few minutes. The waiting rooms pick back up. Our one room won't heat or cool page covers this for every brand.
And if a code check shows 00, that means no active malfunction code was found. It is the opposite of an error.
The heating codes, and what each one asks of you
A5 is the one most specific to heating. In heating mode it means the system is holding back heat, the "peak-cut" control, because pressure climbed too high. The usual cause is air that cannot move. Daikin's homeowner steps: turn the unit off, clean the washable indoor filter, and make sure nothing blocks the supply or return air. Furniture against the indoor unit counts.
EA means the unit could not confirm switching between cooling and heating. That is the four-way (reversing) valve. The symptoms are poor heat, or air at room temperature when you asked for warm. Daikin's step is to set every indoor head to the same mode, turn the system off and reset power once. If EA comes back, or the system will not switch between heat and cool at all, stop there. That is a technician's diagnosis.
J6, H9 and U4 are sensor and communication faults. J6 is the outdoor coil sensor, and without it the unit can lose its judgment about when to defrost. H9 is the outdoor air sensor, so the system cannot tell how cold it is outside and protects itself. U4 means the indoor and outdoor units are not talking reliably. For all three, Daikin's guidance is one power cycle at the breaker or disconnect, and if the code returns, stop resetting and schedule service.
Blowing cold air in heat mode?
Work through it in this order:
- Is it defrosting? Cool air from the head for a few minutes, with steam at the outdoor unit, is defrost. It ends on its own.
- Is the mode actually HEAT? Not AUTO, COOL, DRY or FAN, and the setpoint several degrees above the room.
- Does it cool normally but never heat? That points at the reversing valve, which is what EA reports. One reset, then a technician.
Know your Daikin's cold-weather floor
Every heat pump has a published outdoor temperature below which it stops heating to protect itself. On a Daikin, the floor depends heavily on the line. From the manufacturer data behind our model pages:
| Daikin line | Rated to heat down to |
|---|---|
| AURORA R-32 (single-zone and multi-zone) | -13°F |
| ATMOSPHERA R-32 | -13°F |
| OTERRA R-32 | 5°F |
| Standard multi-zone R-32 | 5°F |
That is an 18-degree difference. An OTERRA that stops heating at 0°F is working as designed, and so is an AURORA at -15°F. Below its floor, reduced or paused heat is the specification, not a breakdown, and the fix is backup heat or a colder-rated system, not a repair. Check your exact model on its page in the product finder. If you are choosing now, our best cold-climate mini splits compares the lines that keep heating when it matters.
Safe checks, in order
- Read the display for DEFROST, 3-minute standby, mode conflict or 00.
- Mode and setpoint: HEAT, several degrees above room temperature.
- On multi-zone, match the modes on every head.
- Clean the washable indoor filter and clear the supply and return air. This is Daikin's first step for A5.
- Clear snow from around the outdoor unit's base. Do not chip ice from the coil, and keep the power off while you work near it.
- Check the outdoor temperature against your line's floor (table above).
- Reset power once, not repeatedly. Repeated cycling restarts the standby timer and hides the pattern a technician needs to see.
When to stop and call a technician
U0 means stop using the system. It signals a refrigerant shortage. Current Daikin systems use R-32, which is mildly flammable, so treat U0 as a possible leak: stop heating and cooling, ventilate the room, keep flames and sparks away, and do not keep resetting it. It stays off until a licensed technician has checked the refrigerant circuit.
Call as well if:
- EA, J6, H9 or U4 comes back after one reset;
- A5 returns after you have cleaned the filter and cleared the airflow;
- the outdoor coil stays iced over after a defrost cycle has finished;
- heat has faded gradually over weeks rather than stopping all at once. That pattern points to refrigerant charge, and refrigerant work is certification-gated.
Daikin publishes 61 codes in total. Look yours up in the Daikin error-code library so you can tell the technician exactly what the unit is reporting. Daikin ties its warranty to a qualified dealer installation, so a Daikin dealer is the natural first call: they can also tell you whether the part in question is still covered.
Cooling problems instead? See Daikin mini split not cooling. Every brand's heating checks are in mini split not heating.