Daikin 7H-06 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin 7H-06 fault code mean?
The 7H-06 code on Daikin Altherma heat pumps signals that the system has detected insufficient water flow through the heat exchanger during heating or defrost operation. When circulation drops below the threshold the controller expects, it triggers a protective shutdown and displays this fault rather than risk damage to internal components. This is a safety feature — it does not necessarily mean the heat pump itself has failed, but it does mean something is preventing water from moving around the system at the required rate.
General guidance only — not a substitute for professional advice, and not certified by an heat pump engineer. Always have your specific appliance assessed by a qualified professional. Any heat pump work must be carried out by an MCS-certified heat pump engineer. If you notice a refrigerant leak, a burning smell or water leaking from the unit, switch it off at the isolator and call an MCS-certified heat pump engineer. Refrigerant work must be carried out by an F-Gas registered engineer.
Common causes
- Blocked strainer or clogged magnetic filter Common
Over time, debris, magnetite and sludge accumulate in the system strainer or magnetic filter. As the blockage grows, water flow is progressively restricted until it falls below the level required for normal operation. This is the single most common trigger for 7H-06 and is often discovered during a routine service visit.
- Trapped air causing an airlock Common
Air pockets in the pipework or at a high point in the circuit can significantly disrupt water circulation. Even a partial airlock can cause erratic or reduced flow, and the heat pump interprets this as a flow abnormality. Bleeding radiators and low points in the circuit often clears the fault temporarily, though a recurring airlock usually points to a deeper issue such as low system pressure.
- Low system pressure Common
If the system pressure has dropped below around 1 bar, the circulation pump struggles to maintain adequate flow. This is easy to check on the pressure gauge mounted on the unit or on the pipework nearby. Topping the system up to approximately 1.5–2 bar frequently resolves the fault.
- Failing or seized circulation pump Sometimes
The internal circulation pump can wear over time, or its impeller can seize — particularly if the system contains heavy sludge contamination. A pump running at reduced speed or not at all will fail to deliver the required flow rate, triggering 7H-06. Signs include the pump running unusually quietly, making a grinding noise, or generating excess vibration.
- Isolation or zone valve accidentally closed Sometimes
A partially or fully closed isolation valve or motorised zone valve anywhere in the circuit will restrict flow. This is worth checking if any recent plumbing work has been carried out or if a zone valve has stuck in the closed position.
- System sludge and contamination Sometimes
Heavy sludge build-up — often presenting as black magnetite or rust deposits — can partially block the plate heat exchanger internally, reducing flow through the core of the unit. If a magnetic filter is already installed and found to be heavily loaded, internal contamination of the heat exchanger should be considered, particularly in older systems with mixed pipework.
- Missing or incorrectly set bypass valve Sometimes
Daikin Altherma systems require a minimum flow rate to be maintained at all times. Without a correctly configured bypass, certain system configurations (such as when all zones are closed) can cause flow to drop to zero, triggering the fault.
- Faulty flow sensor or hydro PCB (A1P) Rare
If all hydraulic causes have been ruled out, the flow sensor itself may be providing a false low-flow reading. Less commonly, the hydro PCB (A1P) may be responsible for an incorrect fault signal. These are engineer-level diagnoses involving component testing and should only be investigated once the pipework circuit has been thoroughly checked.
How to fix it
- Reset the heat pump DIY safe
Switch the unit off at the controller and, if accessible and safe to do so, at the electrical isolator. Leave it powered down for around five minutes, then restart. A transient fault — perhaps caused by a brief air pocket during defrost — may clear on its own. Note whether the fault returns immediately or only after the system has been running for a while, as this helps narrow down the cause.
- Check and restore system pressure DIY safe
Locate the pressure gauge on the unit or the pipework nearby. The reading should sit between 1.0 and 2.0 bar when the system is cold. If it reads below 1 bar, top up using the filling loop (usually a braided hose connecting the mains cold supply to the heating circuit) until you reach approximately 1.5 bar. Consult your system's user guide if you are unsure where the filling loop is. Once topped up, restart the unit and monitor for the fault.
- Bleed trapped air from radiators and the system DIY safe
Work through each radiator from the ground floor upward using a bleed key. Open each bleed valve slowly until water — not air — comes out consistently, then close it. After bleeding, recheck the system pressure and top up again if it has dropped. Also check for any bleed points on the unit itself or on the buffer cylinder, if fitted.
- Clear snow, leaves or debris from around the outdoor unit DIY safe
Ensure the area around the outdoor unit is clear. While this does not directly cause a water flow fault, a blocked outdoor unit can trigger defrost cycles more frequently, during which flow abnormalities are more easily detected by the controller.
- Inspect and clean the strainer and magnetic filter heat pump engineer
The Y-strainer and any magnetic filter fitted on the return pipe should be inspected and cleaned. This involves isolating sections of pipework and handling pressurised water. While a competent DIYer may be able to clean a magnetic filter if they are familiar with the procedure, this step is ideally carried out by a heating engineer who can also check for signs of wider contamination.
- Check all isolation and zone valves DIY safe
Trace the visible pipework and check that all isolation valves (quarter-turn or gate type) are fully open. If motorised zone valves are fitted, confirm they are not stuck in a closed position — sometimes these can be heard clicking open and closed, or their manual override lever can be used to confirm operation. Consult your installer's schematic if available.
- Have an MCS-certified engineer assess the circulation pump and bypass configuration heat pump engineer
If the above checks do not resolve the fault, the circulation pump should be tested for correct speed, flow rate and impeller condition. The engineer will also verify that a bypass is correctly installed and set to maintain minimum flow when zones close down. Pump replacement or bypass installation are both straightforward jobs for a qualified engineer but are not suitable for DIY.
- Request flow sensor and hydro PCB (A1P) diagnostics heat pump engineer
If the hydraulic circuit checks out correctly, the engineer should test the flow sensor resistance and connections, and verify the hydro PCB is operating as expected. Faulty sensors or PCBs require replacement by a qualified engineer. Refrigerant circuit components such as the expansion valve or compressor are sealed and must only be handled by an F-Gas registered engineer.
- Contact an MCS-certified heat pump engineer heat pump engineer
If the fault persists after your own checks, book a visit from an MCS-certified heat pump engineer — ideally one with Daikin Altherma experience. If your unit is still within the 5-year warranty period (available when installed by a Daikin D1 or D2 registered installer), contact Daikin UK directly before arranging any third-party engineer visit, as unauthorised attendance may affect warranty cover.
Parts you may need
- Circulation pump (Grundfos or equivalent OEM) · from £140
- Flow sensor / flow switch · from £65
- Y-strainer replacement cartridge · from £25
- Magnetic filter (e.g. Fernox TF1 or Magnaclean Pro) · from £75
- Hydro PCB A1P (Daikin OEM) · from £320
- Bypass valve (automatic or manual) · from £55
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£550, depending on the underlying cause.
Frequently asked questions
Can I fix Daikin fault code 7H-06 myself?
Some of the initial checks are homeowner-safe: restoring system pressure, bleeding trapped air from radiators, and restarting the unit. If those steps clear the fault and it does not return, no further action may be needed. However, if the fault comes back — or if the cause turns out to be a blocked strainer, failing pump, missing bypass or faulty sensor — you will need a qualified engineer. These are not jobs to attempt without the right tools and training.
How much does it cost to repair a Daikin 7H-06 fault in the UK?
For straightforward cases — such as cleaning a blocked filter or correcting system pressure during an annual service — the cost may be minimal or included in a service visit. A dedicated call-out with diagnostic work typically starts around £150–£250. If the circulation pump needs replacing, expect £300–£500 including parts and labour. A full system power flush, which is sometimes necessary when heavy sludge contamination is found, typically costs £350–£600. Major components such as the hydro PCB or heat exchanger are less common causes but can cost significantly more — your engineer will advise if these are involved.
Why does my Daikin Altherma keep showing 7H-06 after I reset it?
A fault that clears on reset but returns after a short period of operation almost always indicates an underlying hydraulic problem that has not been addressed. The most likely culprits are a partially blocked filter, a marginal circulation pump that cannot sustain flow once it warms up, or a recurring airlock caused by low system pressure. Repeated resets without fixing the root cause can put unnecessary strain on the compressor and heat exchanger, so it is worth booking a diagnostic visit if the fault keeps coming back.
Does a 7H-06 fault mean my Daikin heat pump needs a power flush?
Not necessarily — but it is worth considering, particularly if the magnetic filter or strainer is found to be heavily loaded with sludge or magnetite. A power flush is most likely to be recommended if there are visible signs of heavy contamination, if the system has never been flushed, or if the heat exchanger itself is suspected to be partially blocked. Your engineer should inspect the filter contents first, as this gives a good indication of overall system cleanliness before committing to the cost of a flush.