Daikin 89 fault codewhat it means and how to fix it
Heat exchanger frozen. 89-02 and 89-03 are warnings that reset themselves; three of them within half an hour of each other lock the unit out with 89-01, which needs an engineer.
Take care
What 89 means
The 89 family is the Altherma protecting the plate heat exchanger where refrigerant meets your heating water, and the sub-code tells you how far it has got. The service manual gives 89-02 as a warning triggered when the condensing temperature falls below 0 °C during space heating, or the liquid refrigerant thermistor reads 0 °C or lower during heating or hot water; the unit stops and resets automatically. 89-03 is the neighbouring warning. And 89-01, the one with teeth, is declared when 89-02 or 89-03 has occurred three times with less than thirty minutes between each warning: the unit stops and stays stopped until it is manually reset. Why a heat pump would drive its own exchanger toward freezing is the useful part. In heating mode the refrigerant should be giving heat to the water and condensing at a comfortable temperature.
If the water is barely moving — low flow, low pressure, air in the exchanger — or if the refrigerant side is wrong, the refrigerant temperature at the exchanger collapses, and water in a plate exchanger at 0 °C is a cracked exchanger waiting to happen.
Daikin’s checklist for 89-01 reflects both possibilities. It opens with the sensors that could be lying — the inlet water thermistor, the outlet water after heat exchanger thermistor, the refrigerant liquid thermistor — then the hydro PCB, then the refrigerant circuit: stop valves open, correct charge, a clogged circuit, non-condensables, and finally water flow too low. For an owner the pattern is familiar from every other Altherma water code: pressure, recent work, filter, zones. The difference is urgency. A unit that has locked out on 89-01 has been close to freezing its exchanger three times in an hour, and repeatedly resetting it to get heat is the one thing that turns a flow problem into a replacement exchanger.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Water flow too low | The last item on Daikin’s list but the commonest real cause. A blocked filter, closed zones or low pressure leave the exchanger with too little water to warm the refrigerant. | Common |
| A thermistor reading wrongly | Daikin’s first three checks are sensors: inlet water, outlet water after the exchanger, and refrigerant liquid. A false 0 °C reading produces the code without any ice. | Common |
| Refrigerant circuit fault | Stop valves, charge, blockage and non-condensables are all on Daikin’s list. A short charge lets the exchanger run cold; certified work to investigate. | Occasional |
| Hydro PCB fault | Daikin’s fourth check. The board that reads the thermistors and drives the pump, established by an engineer once the sensors test good. | Occasional |
What to try yourself
Read the system pressure and note it. Low pressure and low flow arrive together, and flow is on Daikin’s list.
Note the sub-code. 89-02 or 89-03 once, clearing itself, is the unit protecting the exchanger and may not recur. 89-01 is three of those in half an hour and will not clear on its own.
Do not keep resetting 89-01 to get the heating back. Each reset runs the exchanger back toward freezing, and a frozen plate exchanger is a large repair.
If the heat pump is in an unheated space and the weather is below freezing, tell your installer that too. A stopped heat pump with water standing in it has its own frost risk.Book your installer and give them the sub-code, the pressure and any recent work. Sensors, flow and the filter are theirs; the refrigerant items need F-Gas certification.
Get an F-Gas certified heat pump engineer to look at your Daikin 89
We do not pass enquiries to a repair firm, so there is no form here. When you book an F-Gas certified heat pump engineer, tell them the make, the model and the exact code or message on the display, and ask whether they carry parts for this make — that is what turns one visit into a repair rather than a quote.
What it costs to fix
Typical repair cost
£90–£900
Time on site
15 minutes
An installer visit is typically £90 to £180 and covers pressure, purging and a filter clean. A thermistor is inexpensive. A refrigerant-side fault needs an F-Gas certified engineer, and a plate heat exchanger damaged by freezing is the top of the range.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 28 September 2026
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Related Daikin fault codes
- Ice on the outdoor unitGet it checkedNormal in cold damp weather, and the unit clears it itself. Daikin specifically forbid helping — no hot water, no de-icer, no scraping.Related: defrost and icing
- Bill has jumpedGet it checkedThe most important heat pump fault has no code. If your electricity cost has stepped up with no change in habits, the backup heater is probably doing the work.Related: same brand
- 7HGet it checkedA water flow problem. The sub-code matters more than the code: 7H-01 clears itself, 7H-04 to 7H-06 need a manual reset, 7H-08 is the pump, and 7H-07 is the unit freeing a stuck pump.Related: same brand
- Water at the tap is too coldGet it checkedDaikin give two causes and a remedy that costs money. Before using it, check what your schedule is actually asking the cylinder to do.Related: same brand
- U0Get it checkedShortage of refrigerant in the Altherma outdoor unit. Daikin’s own checklist ends with a leak test, the circuit is sealed, and on an R32 unit this is F-Gas certified work by law.Related: same brand
- U4Get it checkedIndoor/outdoor unit communication problem. Daikin’s checks start with the power supply and the wiring between the two boards, and the published reset is a power reset at the outdoor unit.Related: same brand
Own a Daikin heat pump? Save it and its codes come first next time.
Related guides
Common questions about Daikin 89
Is the heat exchanger actually frozen?
Not necessarily, and Daikin’s newer wording says so: the Altherma 3 M installer guide lists these rows as "Heat exchanger freeze-up protection activated", not "frozen". Daikin trigger 89-02 on temperature readings — condensing temperature or the liquid refrigerant thermistor at 0 °C — and their first three checks are the thermistors themselves. The code means the readings say freezing is close, which is either true or a sensor fault, and both need looking at.
Why did it clear and come back?
Because 89-02 and 89-03 are self-resetting warnings. Daikin publish that three of them within thirty minutes of each other become 89-01, which is a lock-out. If you are seeing the warning clear and return, the lock-out is coming unless the cause is found.
Will the backup heater keep me warm meanwhile?
Depending on how the system is configured it may, and Daikin publish that electricity consumption will then be considerably higher. It is a reason to treat the visit as prompt rather than routine, not a reason to keep resetting the heat pump.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.