L4Daikin · VRV IV RXTQ-TA / RXTQ-TB · Heat Pump

Daikin VRV IV RXTQ-TA / RXTQ-TB error code L4

Radiation fin temperature rise abnormality

Needs attention soon

Also written as heat sink, overheat, inverter temperature, L4

Which models this applies to. Outdoor unit

Quick answer

On Daikin VRV IV RXTQ-TA / RXTQ-TB, L4 is a fault. It means radiation fin temperature rise abnormality. A first thing to check: A blocked or dirty outdoor coil reducing airflow over the inverter heat sink.

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: Check the outdoor coil for dirt and the discharge grille for debris, since reduced airflow over the inverter is the first thing to rule out.

Checked 2026-09-26

What L4 means on this model

The inverter heat sink fins have risen to a temperature the board will not survive, so the unit has shut itself down to protect the electronics. This is a heat protection fault rather than a refrigerant fault, so the causes are airflow and electronics: a dirty coil, a failed fan, a confined installation or a very high ambient temperature.

Symptoms you will notice

Outdoor unit shows L4 and the system stops
The fault happens in hot weather or after the unit has been running a long time
The outdoor unit is in a tight space or against a hot wall
The outdoor coil is dirty or the fan is not moving

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 blocked or dirty outdoor coil reducing airflow over the inverter heat sink
A failed or slow outdoor fan motor
A failed condenser fan capacitor
The unit installed in a confined space with poor discharge airflow
A very high ambient temperature beyond the unit rating
A failed inverter heat sink fan where one is fitted
Debris blocking the unit discharge grille

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.

Check the outdoor coil for dirt and the discharge grille for debris, since reduced airflow over the inverter is the first thing to rule out.
Confirm the outdoor fan is running at full speed.
Check whether the unit has adequate clearance and discharge air path, and whether it is reflecting heat off a wall or a roof.

Do not do these

×Do not keep restarting the unit on L4. Each restart re-runs the electronics at a temperature that has already damaged them.
×Do not enclose or box the outdoor unit to tidy the installation. That removes the discharge airflow this protection depends on.
×Do not spray the outdoor coil with a high pressure hose, which bends the fins and makes the airflow problem worse.

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.

Coil cleaning, clearing debris and checking clearances are reasonable homeowner tasks. Fan and capacitor replacement is a technician job.

What it costs to fix

Parts

Outdoor fan motor $300 to $700. Fan capacitor $30 to $80.

Labor

One to three hours to restore airflow or replace the fan parts.

DIY or technician