If your LG Multi V system is showing error 204, the outdoor unit has stopped receiving a signal from the heat recovery unit.
What this means for your building
On a heat recovery Multi V system, the heat recovery unit is the branch box that decides where refrigerant goes. It is the component that lets your conference room cool while an office on the same system heats.
For that to work, the outdoor unit has to be in constant communication with it.
Error 204 means that conversation has stopped. The outdoor unit is issuing instructions and getting nothing back, so it can no longer control how refrigerant is routed.
Why this matters more on a heat recovery system
A heat pump system has one mode at a time — everything heats or everything cools.
A heat recovery system was specified precisely because that was not acceptable for your building. Different zones need different things simultaneously, and the heat recovery unit is what delivers that.
When it stops responding, you lose the capability you paid extra for. Zones receive nothing, or the wrong mode, and there is no way for the system to sort it out on its own.
How urgent is it?
Urgent. Refrigerant routing is not working correctly, which means zones are not being served as intended.
There is no safety hazard and nothing escaping. But the system cannot do the job it was designed for, and unlike a comfort complaint this will not resolve itself.
What it typically costs
Low to medium.
Most 204 calls resolve to power wiring or communication wiring at the heat recovery unit, or terminations that have worked loose. That is labour rather than parts.
The main cost variable is access. Heat recovery units usually sit in ceiling voids, frequently above occupied tenant space. Reaching one may need coordination, ceiling tile work, or out-of-hours attendance — and on a large installation there may be several to check.
Cost rises where the heat recovery unit PCB itself has failed.
What causes it
- Power wiring problems at the heat recovery unit — it cannot communicate if it is not powered
- Communication wiring damaged or disconnected — often during ceiling work by other trades
- Incorrect connections following a repair or fit-out
- Loose or corroded terminals at either end
- Heat recovery unit PCB fault
- Addressing or configuration errors after equipment was changed
That second cause is the one we find most. Heat recovery units live in ceilings that other trades work in regularly, and the cabling is easy to disturb without anyone noticing.
What happens if you leave it
Zones stay wrong.
Some areas get nothing. Others may receive heating when they asked for cooling, because the system cannot direct refrigerant properly. Tenants report it as a comfort problem, and it gets chased as one — thermostats checked, indoor units inspected — while the actual fault is a communication link in a ceiling void.
There is also a knock-on: without the heat recovery unit responding, related commissioning routines such as pipe detection cannot complete either.
What we check
- Verify power at the heat recovery unit — the simplest cause and worth confirming first.
- Inspect communication wiring between the outdoor unit and heat recovery unit.
- Check terminations at both ends for looseness and corrosion.
- Confirm connections are correct, particularly if work has been done recently.
- Establish what changed — ceiling work and fit-outs are common origins.
- Test the heat recovery unit PCB once wiring and power are confirmed.
- Verify addressing and configuration, since these can be disturbed by equipment changes.
What you can tell us before we arrive
- Has there been ceiling work? The most common origin, and it is rarely connected to the fault by whoever reports it.
- Which zones are behaving oddly? Helps identify which heat recovery unit is involved.
- Do you know where your heat recovery units are? Access planning saves real time on site.
- Any recent electrical work that may have interrupted power to ceiling equipment?
Related codes
- 200 — Auto pipe detection failure. Cannot complete if the heat recovery unit is not communicating.
- 237 — Indoor to outdoor communication PCB error. Related communication territory.
Get the link restored
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Related codes
Error 200 is auto pipe detection failure. The system cannot work out which indoor unit is on which heat recovery port — and it recurs after any PCB replacement.
Error 237 means the indoor communications PCB received nothing from the outdoor unit for over three minutes. An RS-485 communication fault.
Frequently asked questions
What does error code 204 mean on an LG Multi V system?
The outdoor unit is not receiving a signal from the heat recovery unit. Communication between them has failed, which means the system can no longer control how refrigerant is routed to individual zones. On a heat recovery system that is the capability you specifically paid for.
What is a heat recovery unit on a Multi V system?
It is the branch box that routes refrigerant to each indoor unit, and it is what allows one zone to heat while another cools simultaneously. The outdoor unit must communicate with it constantly to direct refrigerant to the right places.
What causes a 204 communication error?
Most commonly power wiring or communication wiring problems at the heat recovery unit, incorrect connections, loose or corroded terminals, or a fault on the heat recovery unit PCB. Damage during ceiling work is a frequent origin. These units sit in ceilings other trades work in regularly.
Will my system still cool with a 204 error?
Not reliably. Without the heat recovery unit responding, the system cannot route refrigerant to zones as intended. Some areas may receive nothing, and simultaneous heating and cooling — the reason a heat recovery system was specified — stops working.
Where is the heat recovery unit located?
Usually in a ceiling void, frequently above an occupied tenant space. That location matters for access, and it is also why these units are vulnerable to disturbance during ceiling work by trades unrelated to the air conditioning. Knowing their locations in advance speeds up any visit.
How much does a 204 error cost to fix?
Usually toward the lower end, since most cases resolve to wiring or terminations rather than components. The main variable is access, because reaching a heat recovery unit in an occupied ceiling can require coordination or out-of-hours attendance. A large installation may have several to check.