Daikin Water at the tap is too coldwhat to check
Daikin give two causes and a remedy that costs money. Before using it, check what your schedule is actually asking the cylinder to do.
Take care
What this means
This is one of only four symptom entries Daikin put in their householder documentation, which tells you how common it is. Their two published causes are unusually high hot water consumption, and the hot water setpoint being too low. Their remedy is to use the powerful hot water operation, and they attach a warning to it that owners should read before pressing anything: it consumes extra energy. That warning is the whole point of this page. A heat pump makes hot water differently from a boiler, and the difference is what catches people out. A combi boiler heats water as you draw it and never runs out.
A heat pump heats a cylinder in advance, slowly and at a modest temperature because that is what makes it efficient, and when the cylinder is empty it is empty. So the honest first question is not what has failed but what changed. A visitor staying, a bath instead of a shower, or a run of loads through the washing machine will empty a cylinder that has coped fine for two years, and the system is behaving correctly. The second question is what the schedule is doing. Hot water reheats are almost always timed, frequently to overnight cheap-rate electricity, and a schedule that was set up around one household routine will not suit a different one.
A tariff change, a clock going forward, or somebody adjusting the times can leave the cylinder reheating at three in the morning and running out by six in the evening. None of that is a fault, and none of it needs an engineer. What does need one is a cylinder that no longer reaches temperature at all on its normal schedule, a system that has quietly started using the immersion heater to make hot water instead of the heat pump, or hot water that has stopped while the heating still works. Those are real, and the middle one is expensive to leave alone because it is invisible on everything except the bill.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Unusually high hot water consumption | Daikin’s first published cause. A cylinder holds a fixed amount, and an extra person in the house or a bath instead of a shower will empty it without anything being wrong. | Common |
| The hot water setpoint is too low | Daikin’s second published cause. A low setpoint is efficient and often deliberate, but it leaves less usable water in the cylinder because less cold has to be blended in. | Common |
| The reheat schedule does not suit how you use hot water | Reheats are usually timed to cheap-rate electricity. A schedule that worked for one routine will not work for another, and it looks exactly like a failing cylinder. | Common |
| The system has stopped reaching temperature | The genuine fault case. If the cylinder no longer gets hot on its normal schedule, or the immersion has started doing the work, that needs an installer rather than a settings change. | Occasional |
What to try yourself
Ask what changed. More people in the house, a different washing routine, or a bath where there used to be showers will all empty a cylinder that was previously fine.
Look at the hot water schedule on the controller and check when it is set to reheat. If it is timed to overnight electricity, running out by evening is the schedule rather than a fault.
Check the hot water setpoint. Daikin name a low setpoint as one of their two causes, and raising it slightly gives you more usable water.
Use the powerful hot water operation for a one-off need, such as visitors, but understand what it costs. Daikin publish that it consumes extra energy, because it is usually the immersion heater doing the work rather than the heat pump.
Do not leave powerful operation running as a permanent fix for a cylinder that has stopped performing. It hides the fault and it is the most expensive way to heat water in the house.If the cylinder no longer reaches temperature on its normal schedule, call your installer. Say what temperature it is reaching and when, because that is what they need.
Get an F-Gas certified heat pump engineer to look at your Daikin heat pump
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
£0–£250
Time on site
40 minutes
Nothing if it is consumption or a schedule, which covers most cases. An installer visit if the cylinder no longer reaches temperature, because that is a sensor, a diverter valve or a coil rather than a setting.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Daikin fault codes
- AHGet it checkedThe tank disinfection cycle did not complete: the setpoint was not reached within six hours or not held long enough. The unit keeps running, and Daikin’s first cause is hot water drawn mid-cycle.Related: hot water and cylinder
- 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
- 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: 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
- 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
Should I just raise the hot water temperature?
A little, perhaps, and Daikin do name a low setpoint as a cause. But every degree costs efficiency, because the heat pump has to work harder for a smaller return the hotter it goes, and above a certain point the immersion heater takes over. Fixing the schedule is usually cheaper than raising the temperature.
Why does the water run out when it never used to?
A cylinder holds a fixed volume and a heat pump refills it slowly, so any increase in use shows up immediately. That is the most likely answer if nothing about the system changed. If your usage genuinely has not changed, look at the schedule next, and only then treat it as a fault.
Is the immersion heater making my hot water?
It might be, and that is worth establishing because it is invisible except on the bill. Daikin publish that when the backup or booster heater takes over the heat load, electricity consumption will be considerably higher. If your hot water is fine but your bill has stepped up, ask your installer to check what is actually heating the cylinder.
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.