Daikin 7H-05 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin 7H-05 fault code mean?
The 7H-05 fault code on Daikin Altherma heat pumps indicates that the system has detected insufficient water flow through the heat exchanger during space heating operation. The unit monitors flow continuously, and when flow drops below the minimum threshold — or a sensor reports that it has — the system locks out to protect the heat exchanger and compressor from running dry or overheating. Note that this code is specific to the Daikin Altherma air-to-water and water-to-water ranges; on other Daikin product lines, a 7H reading is not a valid code and may instead point to a malfunctioning main PCB.
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
- Closed or partially closed isolating valve Common
One of the most frequent triggers. A valve somewhere in the heating circuit — perhaps closed during maintenance and not fully reopened — restricts flow enough to trip the fault. Check all manual valves on both the flow and return pipework are fully open.
- Air trapped in the water circuit Common
Air locks in the pipework or within the unit itself reduce effective flow and can cause the flow sensor to read incorrectly. This is particularly common after a system refill or if pressure has been low for a period. Bleeding radiators and checking the automatic air vents on the unit can resolve this.
- Low system pressure Common
If the heating circuit pressure has dropped significantly below the recommended level (typically 1.0–2.0 bar when cold), the pump may struggle to circulate water adequately. Low pressure is often caused by a small leak or gradual air release.
- Blocked or dirty water filter/strainer Common
The inline strainer or filter protecting the unit can accumulate debris over time, progressively increasing resistance in the circuit and reducing flow. This is a straightforward fix but requires the circuit to be isolated first.
- Bypass valve fault or absence Sometimes
Daikin Altherma systems require a correctly configured bypass valve to ensure a minimum flow rate is maintained, particularly when zone valves close. A leaking, seized or incorrectly set bypass — or no bypass at all — is a known cause of repeated 7H faults. UK installers have reported this as the root cause after a succession of 7H-01 and 7H-05 errors.
- Faulty or wired incorrectly flow sensor Sometimes
If the flow sensor itself has failed or its wiring has become loose or corroded, it can report a false low-flow condition even when the circuit is flowing normally. This requires an engineer to check sensor output and wiring continuity.
- Failing circulation pump Sometimes
The internal hydronic pump may be losing performance due to age, scale build-up or bearing wear, reducing flow below the minimum threshold. An engineer can check pump head pressure and current draw to identify this.
- Faulty 3-way diverter valve Sometimes
The 3-way valve that switches between space heating and domestic hot water circuits can stick or fail partially, disrupting flow in the heating circuit. This is more likely on older units or where water quality is poor.
- Freezing conditions affecting outdoor pipework Sometimes
In cold UK winters, any external pipework that is not adequately insulated can partially freeze, restricting flow. The fault may clear naturally once temperatures rise, though persistent freezing suggests an insulation issue.
- Faulty hydronic PCB (A1P) Rare
In a minority of cases, the hydronic control board itself is responsible — either misreading the flow sensor signal or failing to command the pump correctly. PCB failure is relatively rare and is typically only diagnosed after other causes have been ruled out.
How to fix it
- Check the system pressure gauge on the unit or heating circuit DIY safe
Look at the pressure gauge on your heat pump or heating manifold. It should typically read between 1.0 and 2.0 bar when the system is cold. If it is below 1.0 bar, top up via the filling loop until the gauge reads around 1.2–1.5 bar, then close the filling loop fully. If pressure drops again quickly, there may be a leak — call an engineer.
- Inspect all visible isolating valves in the heating circuit DIY safe
Walk around your plant room or airing cupboard and check that all manual valves on the flow and return pipework are in the fully open position. A valve that is even slightly closed can cause enough restriction to trigger this fault. Do not adjust any valves you are uncertain about.
- Bleed the radiators and check air vents DIY safe
Using a radiator bleed key, release air from each radiator starting from the ground floor and working upward. If air has been trapped in the system, this can restore adequate flow. After bleeding, recheck the system pressure and top up if it has dropped below 1.0 bar.
- Clear any debris or obstructions around the outdoor unit DIY safe
Check the outdoor unit for leaves, snow, ice or any objects that may have accumulated around the casing or fan grille. While this code relates to water flow rather than airflow, ensuring the outdoor unit is unobstructed is good practice before calling an engineer.
- Perform a system restart from the controller DIY safe
Once you have completed the checks above, attempt a restart from the Daikin user interface or controller. If your installer has shown you how to reset fault codes, follow that procedure. Alternatively, switch off the unit at the indoor isolator, wait approximately 30 seconds, and switch back on. Monitor to see whether the fault returns. If it does within a short time, do not keep resetting — repeated resets without resolving the underlying cause can stress the compressor.
- Engineer to inspect the water filter/strainer and pump performance heat pump engineer
An MCS-certified engineer should isolate the circuit and clean or replace the inline strainer, then assess pump head pressure and current draw to confirm the circulation pump is delivering adequate flow. A pump that is running but underperforming may need replacement.
- Engineer to test the flow sensor and check its wiring heat pump engineer
The engineer should verify the flow sensor output matches actual flow conditions and inspect all wiring connections to the sensor and hydronic PCB (A1P) for corrosion, looseness or damage. If the sensor is reading incorrectly, it should be replaced.
- Engineer to inspect and test the bypass valve and 3-way diverter valve heat pump engineer
The bypass valve setting should be checked and adjusted to ensure minimum flow is maintained when zone valves close. The 3-way diverter valve should be tested for correct operation and replaced if it is sticking or leaking internally. If no bypass is installed, one may need to be fitted.
- Engineer to assess the hydronic PCB (A1P) if all other causes are eliminated heat pump engineer
If all hydraulic components and sensors test correctly, the hydronic PCB itself may be the cause. PCB diagnostics and replacement must be carried out by a qualified engineer using Daikin service software. After any repair, a manual reset via the user interface is required before the unit will restart.
- If the fault persists or recurs, contact an MCS-certified Daikin-authorised heat pump engineer heat pump engineer
Persistent or recurring 7H-05 faults that do not resolve with the checks above require specialist diagnosis. Use an MCS-certified engineer who is also Daikin-trained where possible. Any work on the refrigerant circuit must be carried out by an F-Gas registered engineer. Check whether your unit is within Daikin's warranty period — Daikin UK offers up to five years parts and labour when the unit was installed by a registered Daikin D1 or D2 installer and registered within 30 days at daikin.co.uk/warranty.
Parts you may need
- Daikin Altherma flow sensor · from £65
- Inline water strainer/filter (22mm or 28mm) · from £25
- Daikin 3-way diverter valve · from £145
- Bypass valve (suitable for Altherma) · from £55
- Hydronic circulation pump (replacement) · from £180
- Hydronic PCB A1P (Altherma) · from £320
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–£450, depending on the underlying cause.
Frequently asked questions
Can I fix the Daikin 7H-05 fault myself?
A few basic checks are safe to do yourself: top up the system pressure if it has dropped, bleed any air from the radiators, ensure all isolating valves are fully open, and attempt a controlled restart from the controller. However, if these steps do not clear the fault, the cause is likely a component that needs professional testing or replacement — such as the flow sensor, circulation pump, bypass valve or hydronic PCB. Attempting to dismantle any part of the unit yourself will void your warranty and could cause further damage.
How much does it typically cost to repair a Daikin 7H-05 fault in the UK?
Most homeowners with this fault pay somewhere between £150 and £450 including parts and labour. A straightforward fix such as cleaning the strainer, bleeding the system or replacing the flow sensor sits at the lower end. Replacing the bypass valve or 3-way diverter valve typically falls in the middle of that range. If the hydronic PCB (A1P) needs replacing, costs can rise to £500–£700 once parts and labour are included. Compressor or refrigerant circuit repairs are unrelated to this specific fault code under normal circumstances.
Why does my Daikin Altherma keep showing 7H-05 after I reset it?
If the fault returns quickly after each reset, it means the underlying cause has not been addressed. Common repeat offenders are a partially blocked water strainer, a degrading bypass valve that is not maintaining minimum flow when zone valves close, or a failing circulation pump. Repeatedly resetting without investigating puts unnecessary stress on the compressor. Book an engineer visit if the fault returns more than once or twice.
Is the 7H-05 fault covered under Daikin's warranty?
It can be, depending on the root cause. If a component such as the flow sensor, 3-way valve or hydronic PCB has failed due to a manufacturing defect, it is likely covered. Daikin UK offers up to five years parts and labour warranty for Altherma units installed by a Daikin D1 or D2 registered installer, provided the unit was registered within 30 days of installation at daikin.co.uk/warranty and has been serviced annually by a qualified engineer. Faults caused by poor installation, incorrect system design (such as a missing bypass) or lack of maintenance are generally not covered.