Daikin U2: power supply malfunction or an instantaneous power failure
Daikin U2 is the system-division entry for a power supply malfunction or instantaneous power failure. Learn what the control saw and when a reset is honest.
What this means
In the Daikin malfunction chart, U2 belongs to the system division and reads as a malfunction of the power supply or an instantaneous power failure. That covers both a supply that briefly disappeared and a supply that is present but outside what the drive will work with, which is why one U2 after a storm and a U2 that repeats every day mean unrelated things.
Equipment and model context
Daikin equipment covered by the SM-TS3 malfunction chart, where the U division reports system-level conditions across room air, SkyAir, and VRV
- RXS series
- RZQ series
- RXYQ series
- FTXS series
The reading is taken from the Daikin After Sales Service chart, where the U division covers system conditions rather than one unit. Some Daikin equipment, including the room air lines, presents a related shortage entry as U0, so confirm which digit is displayed before treating the fault as electrical.
What you may notice
- The system stops and displays U2 following a power cut, a storm, or work on the building supply.
- The code appears without any external event, and returns each time the equipment is restarted.
- Other equipment on the property shows signs of an unstable supply, such as clocks resetting or protective devices operating.
Likely causes
- A momentary interruption in the incoming supply leaves the drive unable to complete its sequence, and the event is recorded rather than ignored.
- Supply voltage sitting outside the range on the data plate, in either direction, presents as a power supply condition to the control.
- A loose or corroded connection in the supply path to the outdoor unit produces the same electrical picture as an unstable grid.
Diagnostic paths
U2 arrived immediately after a known power cut
The property lost power, or the supply flickered during a storm or a grid event, and the code was present when the system was next used.
One restart is reasonable here. If the system runs normally afterwards and the code does not return, the entry recorded an external event rather than an equipment fault.
The code returns every time with no external trigger
No power cut occurred, yet the system reports U2 on restart, and the pattern repeats over days without any change in weather or load.
Stop restarting and arrange service. A repeating supply fault with no external cause points inside the installation, and it needs measuring rather than retrying.
Other equipment in the building is also unsettled
Lights flicker, timers reset, or protective devices operate elsewhere on the property around the same period the code appears.
Report the wider pattern, because the investigation may belong to the electrical installation or the supplier rather than to the heat pump.
Two cases hide behind one number. A brief interruption is an event the control logs and recovers from, while a supply outside its working range is a condition that will keep stopping the equipment until it is corrected.
- TransientSupply vanished for a moment
- RecoveryOne restart restores operation
- PersistentSupply is present but out of range
- No recoveryRestarting changes nothing
| Circumstance | Reasonable reading | Next step |
|---|---|---|
| Single event after a storm | External interruption recorded | One restart and observe |
| Repeats daily, no cut | Supply condition inside the installation | Electrical assessment |
| Follows recent electrical work | A connection disturbed during the work | Return to the installer |
| Whole property affected | Incoming supply quality | Raise with the electrical supplier |
The only Daikin code where a reset is genuinely diagnostic
Most protection codes get worse with repeated restarts, and this site says so on every one of them. U2 is the exception worth stating plainly. Because the entry covers an instantaneous power failure, a single clean restart distinguishes an event that has already passed from a condition that is still present, and that distinction is not available any other way from the room.
The discipline is in stopping at one. If the system runs normally after a single restart and the code does not come back, the record was doing its job. If U2 returns, the supply condition is live, and further attempts only add cycles to a drive that is being asked to start on power it has already rejected.
Why the equipment is fussier than a kettle
An inverter-driven heat pump rectifies the incoming supply into a direct-current bus and builds its own waveform from there. That bus has a working window, and a supply that sags, surges, or disappears briefly moves it outside that window faster than a simple resistive appliance would notice. The equipment is not being delicate; it is protecting semiconductors that fail permanently rather than gracefully.
It also means the fault can belong to the building rather than to the unit. A shared circuit, an undersized supply run, a loose terminal in an isolator, or a genuinely poor incoming supply all produce the same entry. That is why a U2 that repeats leads to an electrical assessment of the installation as readily as to a heat pump repair. The data plate guide explains where the voltage range for your unit is printed, and the mini-split reset guide covers how to restart safely and how often.
What to give the technician
Tell the technician the outdoor model and serial number, the U2 display, whether a power interruption is known to have occurred, how many restarts were attempted, and whether other equipment in the building is affected.
Safe homeowner checks
- Check whether a power cut, a storm, or electrical work coincided with the code, and write down what you find.
- Confirm that the dedicated isolator and any protective device serving the equipment are in their normal operating position.
- Read the supply voltage and frequency printed on the outdoor unit data plate so the figures are available to service.
Is a reset appropriate?
One restart is the accepted test for this entry because the chart includes an instantaneous power failure. If the code returns after that single attempt, leave the system off and treat the supply as the subject of the investigation.
When to call a technician
- Measuring supply voltage under load, inspecting isolator and terminal connections, and testing the drive input are qualified electrical tasks.
- A protective device that operates repeatedly, a burning smell, or heat at an isolator is a stop condition. Leave the supply off and arrange an electrical inspection.
Questions people ask about this
Is Daikin U2 the same as U0?
No. The U division covers system conditions and the digit selects which. U2 reads as a power supply malfunction or instantaneous power failure, while U0 is published against a refrigerant shortage, which is an entirely different investigation.
Can a power cut really leave a stored code?
Yes. The control records that the supply vanished mid-sequence rather than assuming it was a deliberate shutdown. That is what allows one restart to clear the entry when the interruption has genuinely passed.
Why does U2 keep coming back with no power cut?
A supply that is present but sitting outside the working range produces the same entry as a brief loss. That condition does not pass on its own, so each restart meets the same voltage the drive already refused.
Could an extension lead or shared circuit cause this?
Equipment of this kind is designed for a dedicated supply of the rating on its data plate. Anything that introduces voltage drop under starting load makes the entry more likely and should be raised with an electrician.
Evidence recordHow this page was checked
service manual · checked 2026-09-15
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Daikin Industries technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- service manual
- Scope of the definition
- Daikin equipment covered by the SM-TS3 malfunction chart, where the U division reports system-level conditions across room air, SkyAir, and VRV
- Last checked
- 2026-09-15