A 7H code on a Daikin Altherma is a water flow fault, and low water pressure in the heating circuit is one of the things Daikin’s own troubleshooting list tells an engineer to check. 7H-01 is a general flow problem, 7H-05 means the flow problem happened during space heating, and the unit stops until the cause is dealt with. Check the pressure gauge, look for obvious leaks, and if the code returns, stop resetting it and get an engineer in.
If it keeps coming back, book an engineer rather than topping up or restarting repeatedly. You can book a heat pump repair online or call 0333 041 5130, and our full Daikin Altherma heat pump error codes guide covers every other code.
Please read first: this article is a guide only. We make every effort to keep it accurate, but manufacturers update manuals and codes can differ between models and software versions, so always check the official Daikin Altherma manual for your exact model. Do not attempt anything dangerous or anything that could void your warranty.
What does 7H-01 & 7H-05 mean on a Daikin Altherma heat pump?
Daikin’s service documentation for the Altherma 3 range lists the 7H family as water flow faults. The code is made of two parts: 7H is the fault, and the number after the dash tells you when it happened.
- 7H-01: the system has detected a flow abnormality during operation. The unit stops, and Daikin lists this one as resetting automatically.
- 7H-04: a flow problem while the unit was making domestic hot water. It needs a manual reset from the user interface.
- 7H-05: a flow problem during space heating (or sampling). Also a manual reset.
- 7H-06: a flow problem during cooling or defrost. Also a manual reset.
Daikin’s troubleshooting order for 7H-01 includes “water pressure is too low” as one possible cause. It sits alongside a closed stop valve, air in the circuit, low flow, no bypass, a dirty filter in the shut-off valve, and faulty parts such as the flow sensor, 3-way valve, pump or hydro PCB. So a 7H code does not prove your pressure is low, but low pressure is a sensible first thing to rule out. One installer guide we looked at also describes 7H as “filter or low water pressure”.
Daikin does not publish one universal minimum pressure for every Altherma. Figures depend on the model, so the only number we will quote is from the installer reference guide linked above: for the EHVH11 and 16 models it gives a maximum water pressure of 4 bar and a minimum flow rate of 15 l/min. Your own unit’s documents are what count.
Why does low water pressure happen on a Daikin Altherma?
Sealed heating systems lose a little pressure over time, but a steady or sudden drop always has a reason. The usual ones:
- A slow leak at a radiator valve, pipe joint, underfloor manifold, pump seal or the heat pump’s own connections.
- A weak expansion vessel. If the air side has lost its charge, pressure swings wildly between cold and hot and the pressure relief valve may lift.
- Air in the system. Air makes the gauge read oddly, causes gurgling and can starve the pump of water, which then shows up as a flow fault.
- A stuck or failing automatic air vent that weeps water or lets air in.
- Pressure relief valve (PRV) discharge. If it has opened, water goes down the drain pipe and pressure falls. A damp or dripping discharge pipe is a clue.
- Recent bleeding or radiator work. Bleeding radiators removes air and lowers pressure, so it needs topping back up.
- A blocked strainer or shut-off valve filter. This does not lower pressure, but it gives the same 7H flow fault.
- A faulty sensor or flow sensor. The pressure reads fine on the gauge but the unit disagrees.
It is worth knowing that a closed stop valve or a shut zone can produce the same 7H code with normal pressure, which is why a proper diagnosis beats guessing.
What can you safely check yourself?
- Read the pressure gauge on the indoor unit or hydraulic pipework when the system is cold. Note the figure and the date, so you can see if it is falling.
- Look for visible drips, damp patches, stained carpets or wet floors near the unit, the cylinder, radiators and the pressure relief discharge pipe.
- Check that radiators and any zone valves are open, and that nobody has shut a stop valve near the heat pump.
- Only top up through the filling loop if Daikin’s documents for your model allow it and you are confident doing it. Open the valve slowly, stop at the manufacturer’s figure, and close it fully afterwards. Our guide to a heat pump losing pressure explains what repeated drops usually mean.
- Write down the exact code, the time and what the system was doing. An engineer will want all three.
- Reset once from the controller, following the instructions in your user guide. If the code returns, leave it.
What not to do:
- Do not touch refrigerant circuits or pipework. Refrigerant work is for F-Gas certified engineers only.
- Never remove panels or covers from the outdoor or indoor unit.
- Do not keep adding water until the gauge looks high. Over-pressurising can lift the relief valve and damage components.
- Do not ignore repeated top-ups. A system that needs filling every week or two has a leak or a fault.
- Do not keep resetting a 7H code. The unit stopped for a reason.
When should you call an engineer?
- The 7H code comes back after one reset.
- You are topping up more than occasionally, or the pressure drops again within days.
- Water is coming from the pressure relief valve discharge pipe.
- You can see or hear a leak, or the floor, ceiling or cylinder cupboard is damp.
- The heating or hot water has stopped and the house is getting cold.
- The gauge reads zero, or the pressure swings sharply between cold and hot.
- You have no idea which valve or zone to check.
Book early. A small leak found in October is a cheap fix. The same leak found in January, when the heating is running flat out, tends to arrive with a cold house and a queue for appointments. If the system is still under warranty or an installer guarantee, contact them first so you do not put cover at risk.
How can you stop it happening again?
- Have the system looked at every year. Our annual service checklist shows what a proper service should cover, including pressure, the expansion vessel, filters and the air vent.
- Check the gauge monthly in winter and write the figure down. A slow trend is far easier to act on than a sudden stop.
- Deal with drips early. Our guide to a heat pump leaking water explains where leaks usually start.
- Keep the system clean. Debris blocks strainers and filters, and a dirty circuit may need a heat pump powerflush.
- After bleeding a radiator, check the gauge straight away.
- Do not leave zone valves or stop valves partly closed after maintenance.
Other Daikin Altherma codes you might see with low pressure
| Code | Meaning | First step |
|---|---|---|
| 7H-01 | Flow abnormality during operation (automatic reset) | Check gauge, stop valves and radiators open, then call an engineer if it returns |
| 7H-04 | Flow problem during domestic hot water production | Check the cylinder circuit valves and gauge, reset once |
| 7H-05 | Flow problem during space heating | Check radiators and zone valves open, check pressure |
| 7H-06 | Flow problem during cooling or defrost | Check pressure and valves, then book an engineer |
| C0-00 | Flow sensor malfunction (sensor sees flow after the pump has stopped) | Engineer only: sensor or pump check |
Need help with low pressure on a Daikin Altherma heat pump?
UK Heat Pump Servicing engineers find the leak, check the expansion vessel and air vent, test the flow and carry out heat pump repairs with a 12-month guarantee. We also offer an annual heat pump service and cover plans, so small pressure problems are caught before they stop the system. Contact us or call 0333 041 5130.
Frequently asked questions
Can I clear a 7H code by switching the Daikin off and on?
You can try one reset from the controller, but a 7H code that returns means the fault is still there. Repeated restarts hide the pattern an engineer needs to see, so note the time and code each time.
Is the 7H-01 reset automatic?
Daikin’s service documentation lists 7H-01 as an automatic reset, while 7H-04, 7H-05 and 7H-06 need a manual reset from the user interface. Your model or software version may behave differently.
Will a blocked filter cause the same code?
Yes. A dirty filter in the shut-off valve is on Daikin’s own list of causes for 7H-01. It restricts flow without changing the gauge reading, so pressure alone will not tell you.
Does the heat pump need a bypass?
Daikin’s troubleshooting list includes “no bypass installed in the water circuit” as a cause of flow faults. Whether yours needs one depends on the design, so this is a job for the installer or a service engineer to confirm.
Could a 7H code appear in a heatwave or in summer?
It can. Cooling and defrost have their own code, 7H-06, and any time of year a closed valve or air in the circuit can starve the pump. Season does not cause the fault, but how hard the system is working can expose it.
