On a Panasonic Aquarea, H62 is the water flow fault: the indoor unit’s flow sensor is seeing too little or no water moving through the heat pump. H21 is listed in Panasonic’s service documentation as an abnormal water pressure fault, caused by either a faulty water pressure transducer or a leak in the hydraulic circuit, though it only appears on some generations of unit. First check the system pressure gauge, look for leaks and make sure all isolating valves are open. If the code returns, stop resetting it and call an engineer.
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 Panasonic 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 Panasonic Aquarea manual for your unit. Do not attempt anything dangerous or anything that could void your warranty.
What do H62 and H21 mean on a Panasonic Aquarea heat pump?
H62 is the “water flow switch” or “abnormal water flow” fault. During heating or cooling, the flow sensor in the indoor unit detects incorrect flow or none at all. According to Panasonic’s service documentation, the fault is raised if the condition lasts 10 seconds, and it is ignored for the first 9 minutes after the compressor starts. The listed causes include air trapped in the system, closed isolating valves, a leak or restriction in the pipework, a faulty flow sensor or its wiring, a failed pump, or a fault on the indoor control board.
So H62 is not strictly a “pressure” code, but low pressure is one of the main ways to end up with it. If the system has lost water, the pump has less to move and the sensor sees less flow.
H21 is described in Panasonic’s Polish-language service manual as “abnormal water pressure”, detected after 300 seconds, with a faulty pressure transducer or a hydraulic leak as the listed causes. We could only confirm H21 in one Panasonic document, and other Panasonic code lists we checked do not include it. Treat that as a sign that it depends on the generation and software of your Aquarea, and check which codes your own manual lists before relying on it.
H20 is worth knowing about too. It is a water pump abnormality, raised when the pump runs at an abnormal speed for 5 seconds. A pump that has been idle, has debris in it or is failing can look like a flow problem from the homeowner’s side.
The Dutch and Polish Panasonic documents we reviewed do not give a recommended pressure in bar, so we are not going to quote one. Your installer’s commissioning sheet will show what your system was set to.
Why does a Panasonic Aquarea lose water pressure or flow?
- A leak at a pipe joint, radiator valve, pump connection or the pressure relief valve.
- A faulty expansion vessel that cannot absorb expansion, so pressure spikes and then drops after the relief valve lifts.
- Air in the system, which reduces flow and can make the automatic air vent release water.
- A blocked filter or strainer, restricting flow while the gauge looks fine.
- A discharging pressure relief valve that does not reseat.
- Recent radiator work or bleeding without topping the water back up.
- Closed isolation or zone valves, leaving too little open circuit for the flow.
- A flow sensor, pressure transducer or wiring fault, reporting a problem that is not really there.
- Too little water volume in the heating circuit. Panasonic lists minimum volumes by unit size.
A useful rule of thumb is to separate what you can see from what you cannot. A falling gauge, a damp patch or a dripping valve are things you can see and report. A flow sensor that reads wrongly, a pump running at the wrong speed or a failed pressure transducer are things only a test meter will show. Panasonic’s service checks for H62 involve measuring voltages at the flow sensor and pump connectors, which is firmly engineer work.
Do not assume that the code means the heat pump is broken. Many H62 callouts end with a blocked strainer, a closed valve or air trapped after a radiator was bled. That is good news, because those are far cheaper to fix than a failed pump or board, but they still need someone who knows where to look.
What can you safely check yourself?
- Read the pressure gauge on the hydromodule or pipework and write down the figure, noting whether the system is hot or cold.
- Look for visible drips, wet patches or staining around the indoor unit, cylinder and pipework.
- Check that radiator valves and any zone valves are open.
- Note the full error code and the time it appeared on the controller, so the engineer can see the pattern.
- Top up through the filling loop only if the manufacturer’s manual allows it for your unit and you are competent. Add water slowly, close the loop fully and disconnect it afterwards.
- Read our guide to a heat pump losing pressure for what is normal and what is not.
What not to do:
- Do not touch refrigerant circuits or pipework. Refrigerant work is for F-Gas certified engineers only.
- Do not remove covers or panels on the indoor or outdoor unit.
- Do not keep over-pressurising the system to clear the code.
- Do not ignore repeated top-ups. They mean water is going somewhere.
- Do not use the service settings to run the pump at maximum speed unless an engineer has told you to.
When should you call an engineer?
- H62 or H21 returns after you have checked the pressure and valves.
- Pressure falls again within days of a top-up.
- There is water on the floor, around the unit or at the relief valve outlet.
- The pressure looks right but the code stays, which points to a sensor, pump or PCB fault.
- H20 appears alongside a flow fault.
- You have lost heating or hot water.
Booking early matters. Low flow means the heat pump cannot shed its heat, which puts extra strain on components that are expensive to replace.
How can you stop it happening again?
- Book an annual service. Our annual service checklist covers filter cleaning, pressure checks, the expansion vessel and the pump.
- Deal with small drips quickly. Our guide to a heat pump leaking water explains where to look.
- If the system is sludgy or old, ask about a heat pump powerflush to clear debris that blocks flow.
- Check the gauge monthly and keep a note of readings.
- Make sure the system was commissioned properly, including venting and a check of the expansion vessel. See our commissioning checklist.
Other Panasonic codes you might see with low pressure
These are the water-side codes we could verify from Panasonic service documentation. Code lists vary between Aquarea generations, so check your own manual.
| Code | Meaning | First step |
|---|---|---|
| H62 | Abnormal water flow or flow switch fault | Check pressure, open valves and look for leaks, then book an engineer if it returns |
| H21 | Abnormal water pressure (pressure transducer fault or leak), on some models only | Check the gauge and look for leaks. Call an engineer to test the transducer |
| H20 | Water pump abnormality (speed outside normal range) | Do not keep restarting. Book an engineer to check the pump |
| H99 | Indoor unit freeze protection, with low water flow among the listed causes | Check valves and pressure. Book an engineer promptly |
| H98 | Outdoor high pressure protection, with poor water flow among the listed causes | Book an engineer. This involves the refrigerant circuit |
Refrigerant-side codes such as H63 (outdoor low pressure) are not water pressure faults and need an F-Gas engineer.
Need help with low pressure on a Panasonic Aquarea heat pump?
UK Heat Pump Servicing engineers find the leak, check the expansion vessel and air vent, test the flow sensor and carry out heat pump repairs with a 12-month guarantee. We also offer an annual heat pump service and cover plans to catch problems early. Contact us or call 0333 041 5130.
Frequently asked questions
Can an H62 error clear itself?
It can, if the cause was a temporary air lock. If it keeps returning, the cause is still there. Note when it appears and tell your engineer.
Why does the error appear only when the heating starts?
Panasonic ignores flow faults for the first 9 minutes after the compressor starts, so problems often show up once the unit settles into running. Air, a restriction or a weak pump tends to show then.
Is a minimum water volume important?
Yes. Panasonic specifies minimum system water volumes for its units, and too little water can cause flow and temperature faults. If your installation has lots of zone valves closing, a buffer may be needed.
Can I bleed the radiators to fix it?
Bleeding removes air but also lets pressure fall, so you must top the system back up afterwards. Only do this if you are confident, and recheck the gauge afterwards.
Does the Panasonic warranty cover flow faults?
It depends on the cause and the warranty terms. Keep your service records, as missed servicing can affect cover.
