U2Daikin · VRV IV RXTQ-TA / RXTQ-TB · Heat Pump

Daikin VRV IV RXTQ-TA / RXTQ-TB error code U2

Power supply insufficient or instantaneous abnormality

Needs attention soon

Also written as power supply, brownout, insufficient power, U2

Which models this applies to. System

Quick answer

On Daikin VRV IV RXTQ-TA / RXTQ-TB, U2 is a fault. It means power supply insufficient or instantaneous abnormality. A first thing to check: A supply that is undersized for the connected indoor units.

Applies to: Daikin VRV IV RXTQ-TA / RXTQ-TB; Daikin VRV IV RXTQ heat pump codes · Heat Pump
Type of code: Fault; Urgency: Needs attention soon
First safe check: Measure the supply voltage at the outdoor unit while the system is starting, because a supply often looks acceptable when nothing is running.

Checked 2026-09-26

What U2 means on this model

The supply is not holding up, either because it is undersized for the connected indoor units or because it was interrupted momentarily. This matters more on VRV than on a single split, because one outdoor unit can feed many indoor units and the combined starting current can exceed a marginal supply.

Symptoms you will notice

Outdoor unit shows U2 and the system stops
The system stops when several indoor units start at once
The supply voltage dips when the system starts
Lights dim or flicker when the system starts
The fault is intermittent and often coincides with other equipment starting

Common causes

The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:

A supply that is undersized for the connected indoor units
Supply voltage that is too low or too high
A loose or corroded supply connection
A brownout or momentary power interruption
Other large equipment sharing the same supply
A failed power supply section in the outdoor unit

What you can safely check

These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.

Measure the supply voltage at the outdoor unit while the system is starting, because a supply often looks acceptable when nothing is running.
Count how many indoor units are connected and check whether the supply was sized for the full connected load rather than for one unit.
Check whether the trip happens at the same time as another large appliance starts on the same supply.

Do not do these

×Do not add indoor units to a supply that was not sized for them. This code is often a capacity problem rather than a fault.
×Do not fit heavier fusing or a larger breaker to stop the code appearing.
×Do not measure inside the outdoor unit with the power switch on.

When to call a technician

Book a technician, do not keep resetting it

This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.

The refrigerant circuit is sealed and legally requires licensed handling. Opening it without certification releases refrigerant and can put the whole system in violation of regulation, so a low-pressure or high-pressure fault on this equipment is a call-out, not a weekend job.
If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.

A technician job. Supply voltage measurement under load is not a homeowner task.

What it costs to fix

Parts

Supply cable or breaker $60 to $400 depending on the run and the fault.

Labor

Two to four hours to trace and correct the supply.

DIY or technician