Daikin E3-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin E3-00 fault code mean?
The E3-00 code indicates that the high-pressure switch (HPS) on your primary outdoor unit has triggered a protective shutdown. The '-00' suffix simply identifies this as the first (or only) outdoor unit in the system. In practical terms, the refrigerant pressure on the high side of the circuit has climbed beyond a safe operating threshold, and the unit has locked itself out to prevent internal damage. This is a safety feature working as intended — but it does mean the underlying cause needs to be found and resolved before the system will run reliably again.
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 or dirty outdoor heat exchanger coil Common
Dirt, dust, cottonwood seeds, or compacted debris coating the outdoor coil fins severely reduces the unit's ability to shed heat. As heat builds up in the refrigerant circuit, pressure on the high side rises until the HPS trips. This is by far the most frequent trigger for E3 in UK conditions, particularly after a warm, pollen-heavy summer or if the unit is sited near a fence or dense planting.
- Restricted airflow around the outdoor unit Common
Overgrown vegetation, stored garden equipment, snow accumulation, or a recently fitted enclosure around the outdoor unit can starve the fan of fresh air. The unit then recirculates warm exhaust air, driving up refrigerant discharge pressure and activating the HPS.
- Refrigerant overcharge or restriction in the refrigerant circuit Sometimes
If the system has been recently serviced and too much refrigerant was added, or if there is a partial blockage in the pipework or expansion valve, high-side pressure will be elevated even when airflow is perfectly clear. This requires an F-Gas registered engineer to diagnose with manifold gauges and correct.
- Faulty high-pressure switch (HPS) Sometimes
The HPS itself can develop a fault — either tripping at pressures lower than its rated cut-out point, or failing to reset after pressure normalises. If all airflow and refrigerant checks come back clean, a defective switch is the likely culprit. Replacing it is straightforward for an engineer but not a DIY task.
- Defective PCB or wiring connector issue Rare
A poor connector contact between the HPS and the main control PCB, or a fault on the PCB itself, can cause the unit to register a spurious high-pressure trip. This is less common but worth investigating if the fault returns immediately after a clean bill of health on airflow and refrigerant charge.
How to fix it
- Power down and restart the unit DIY safe
Switch the heat pump off at the controller, then turn off the isolator switch or outdoor disconnect. Wait at least three minutes to allow pressures to equalise, then restore power and restart from the controller. A transient pressure spike — sometimes caused by a brief power fluctuation — can trigger the HPS and a simple reset is all that is needed. If the E3-00 code does not return within an hour of normal operation, monitor the system for the next day or two. If it comes back, move on to the next steps.
- Clear the area around the outdoor unit DIY safe
Walk around the outdoor unit and remove anything that could be restricting airflow to or from the fan. This includes fallen leaves or twigs packed against the coil, overgrown shrubs within half a metre, garden furniture, bin bags, or any temporary covers. Also check for snow or ice build-up blocking the intake or exhaust grille — carefully clear this by hand or with lukewarm water (never boiling). There should ideally be at least 30–50 cm of clear space on all sides and 1–2 metres above the fan discharge.
- Inspect the outdoor coil fins for dirt and debris DIY safe
Look closely at the metal fin array on the outdoor unit. If you can see a visible layer of dust, fluff, pollen, or compacted debris, this is almost certainly contributing to the fault. You can carefully rinse the fins from the outside with a gentle garden hose — work top to bottom and keep the nozzle at least 30 cm away to avoid bending the fins. Do not use a pressure washer. If the coil looks heavily soiled, arrange a professional chemical coil clean with an engineer, which will be more effective and carry no risk of fin damage.
- Check system pressure at the indoor unit or buffer vessel DIY safe
On hydronic heat pump systems, a low water-side pressure can affect heat transfer and contribute to refrigerant-side pressure anomalies. Check the pressure gauge on the indoor unit, buffer vessel, or heating cylinder. Normal operating pressure for most UK heat pump heating circuits is between 1.0 and 2.0 bar (check your system documentation for the exact value). If the pressure is below 1.0 bar, top up via the filling loop in small increments. If pressure drops repeatedly, this suggests a leak that needs a qualified heating engineer to investigate.
- Contact an MCS-certified, F-Gas registered heat pump engineer for further diagnosis heat pump engineer
If the E3-00 code returns after the above checks, the fault almost certainly lies within the refrigerant circuit or an electrical component — neither of which is safe or legal for a homeowner to work on. An F-Gas registered engineer will connect manifold gauges to measure actual high-side pressure, verify the refrigerant charge, test the HPS for correct cut-out and reset values, check connector integrity, and inspect the control PCB if needed. Do not continue running the unit in a fault state; repeated high-pressure trips under load can eventually damage the compressor, turning a modest repair into a much more expensive one.
Parts you may need
- High-Pressure Switch (HPS) · from £45
- Outdoor unit PCB / control board · from £280
- Expansion valve (EEV) · from £120
- Outdoor fan motor · from £150
- Refrigerant (R32 or R410A, per recharge) · from £80
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 £180–£450, depending on the underlying cause.
Frequently asked questions
Is it safe to keep running my heat pump with an E3-00 fault?
No — you should not attempt to override or ignore the lockout. The high-pressure switch has shut the system down deliberately to protect the compressor and refrigerant circuit from damage. Repeatedly forcing a restart without fixing the underlying cause can stress the compressor to the point of failure. A compressor replacement typically costs £1,400 or more on a small system, so it is well worth resolving the E3 fault promptly at a fraction of that cost.
Could the E3-00 fault be covered under warranty?
Possibly, yes. If your Daikin heat pump was installed by a registered Daikin D1 or D2 installer and the warranty was registered within 30 days of installation, you may have a five-year parts and labour warranty. Contact your installer or Daikin UK directly before paying for any repair — it could be resolved at no cost to you.
How much does it cost to fix an E3-00 fault in the UK?
For most people, the repair falls between £180 and £450. A high-pressure switch replacement including parts and labour typically costs £180–£350. If a refrigerant leak is found, a leak repair plus recharge usually runs £350–£600. PCB replacement is a less common outcome but can cost £450–£900. In rare cases where the compressor has been damaged by prolonged high-pressure operation, costs can exceed £1,400 — which is why early diagnosis matters.
What is the difference between E3 and 7H on a Daikin heat pump?
Both codes relate to elevated refrigerant pressure on the high side of the system, but they are triggered differently. E3 is a protective shutdown activated by the physical high-pressure switch — a mechanical safety device that cuts the circuit when pressure exceeds its rated threshold. The 7H code is triggered by the discharge pressure sensor exceeding safe limits as read by the PCB, and is often associated with refrigerant overcharge or a blocked system. In practice, both codes warrant the same response: check airflow, clear any obstructions, then call an F-Gas engineer if the fault persists.