Daikin EA-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin EA-00 fault code mean?
The EA-00 code appears on Daikin heat pumps when the outdoor unit detects a problem with the four-way valve — the component that reverses the refrigerant flow direction to switch the system between heating and cooling modes. The '00' suffix identifies this as the primary logged instance of the fault. When this valve fails or becomes stuck, the heat pump loses the ability to change operating mode and will lock out to prevent further damage. All diagnostic and repair work beyond a basic power reset must be carried out by a qualified engineer.
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
- Stuck or defective four-way valve Common
The four-way valve can become mechanically stuck in one position, or its solenoid coil can fail electrically. Either prevents the refrigerant circuit from switching direction correctly, which the outdoor unit detects as a fault. This is the most frequently identified root cause of an EA-00 code.
- Refrigerant shortage due to a leak Common
Low refrigerant charge alters the pressures in the sealed circuit, which can cause the four-way valve to behave erratically and trigger an EA alarm even when the valve itself is undamaged. A pressure test is needed to confirm or rule this out.
- Faulty outdoor unit PCB Sometimes
The outdoor printed circuit board controls the four-way valve switching signal. If the PCB develops a fault — due to age, moisture ingress or a power surge — it may send an incorrect signal or fail to detect valve movement, generating an EA-00 alarm.
- Defective thermistors Sometimes
Temperature sensors (thermistors) on the indoor or outdoor coil report conditions used to verify that the four-way valve has switched correctly. A sensor reading inaccurately can mimic a valve fault and cause the system to log an EA-00 code.
- Loose or damaged valve coil wiring Rare
The wiring loom connecting the four-way valve solenoid to the outdoor PCB — including connector CN105 in some models — can develop loose terminals or chafing, interrupting the control signal and triggering the fault.
How to fix it
- Switch the heat pump off at the controller, wait two minutes, then power it back on DIY safe
A transient voltage fluctuation or brief sensor glitch can occasionally set a spurious EA-00 alarm. A clean power cycle clears the fault memory and allows the unit to retest itself on startup. If the code returns immediately or within the first heating cycle, move to the next steps — do not continue cycling power repeatedly.
- Check the isolator and consumer unit for any tripped MCB DIY safe
Confirm that the outdoor unit isolator switch is in the on position and that no circuit breaker in your consumer unit has tripped. A partial power interruption can cause the valve to receive an incomplete switching signal, leading to an EA alarm.
- Clear the area around the outdoor unit of any debris, ice or obstructions DIY safe
Leaves, compacted snow or other debris blocking the outdoor unit can affect operating pressures and indirectly trigger refrigerant-related faults. Ensure at least half a metre of clearance on all sides and check that the fan grille is not blocked. Never attempt to remove panels or touch internal components.
- Check system pressure on the heating circuit and top up if low DIY safe
On a wet central heating system, confirm that the system pressure gauge reads within the range shown in your installer documentation (typically 1.0–2.0 bar when cold). If pressure is low, top up via the filling loop according to your system manual. Note that this addresses the heating circuit water pressure, not the sealed refrigerant circuit.
- Call an MCS-certified heat pump engineer to inspect the four-way valve, wiring and coil heat pump engineer
An engineer will check the solenoid coil for electrical continuity, inspect the CN105 connector and associated wiring for damage or loose terminals, and verify that the valve is physically switching when commanded. A faulty coil can often be replaced without disturbing the refrigerant circuit, keeping costs reasonable if caught early.
- Have an F-Gas registered engineer carry out a refrigerant pressure test heat pump engineer
If the valve and wiring check out correctly, the next step is a pressure test of the sealed refrigerant circuit to identify any leak. UK law requires F-Gas certification for any work involving refrigerant. If a leak is confirmed, the engineer will locate and repair it before recharging the system to the manufacturer's specified quantity.
- Allow the engineer to inspect and replace the outdoor PCB or thermistors if required heat pump engineer
Should the valve, wiring and refrigerant charge all prove satisfactory, the outdoor PCB or a thermistor is likely responsible. The engineer will test sensor resistance values against the manufacturer's specification and check the PCB for visible damage. Both components require professional replacement using the correct Daikin-compatible parts.
Parts you may need
- Four-way valve solenoid coil · from £65
- Four-way valve body (full assembly) · from £180
- Outdoor unit thermistor (coil sensor) · from £35
- Outdoor unit PCB · from £320
- CN105 wiring connector/loom · from £25
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–£600, depending on the underlying cause.
Frequently asked questions
Can I keep using my heat pump while it shows EA-00?
No — you should not continue running the system. The EA-00 code indicates the outdoor unit has detected a four-way valve malfunction and has locked out for a reason. Forcing the unit to operate with a stuck valve or low refrigerant can cause the compressor to work against abnormal pressures, potentially turning a relatively affordable repair into a compressor replacement costing upwards of £1,400. Switch the unit off and contact an engineer promptly.
Will a power reset fix the EA-00 code permanently?
Occasionally a one-off power cycle will clear a spurious EA-00 alarm caused by a brief electrical glitch. However, if the code returns after restart — or comes back within a few hours or days — there is an underlying fault that requires professional diagnosis. Repeated resets without investigation will not fix the root cause and may mask a developing problem.
Do I need an F-Gas engineer or an MCS engineer for this repair?
In practice, you need an engineer who holds both MCS certification and F-Gas registration — most established UK heat pump companies have engineers who hold both qualifications. MCS certification covers the overall heat pump installation and service work, while F-Gas registration is the legal requirement for anyone handling refrigerant (for example, conducting a pressure test or regassing the system after a leak repair).
What does an EA-00 repair typically cost in the UK, and can it be much more expensive?
For the most common outcomes — a four-way valve coil replacement, a thermistor swap, or a leak repair and regas — most homeowners pay somewhere between £180 and £600 including parts and labour. If the outdoor PCB needs replacing, costs typically rise to £450–£900. In less common scenarios where the four-way valve body itself requires full replacement or, in a worst case, where compressor damage has occurred due to the fault running unchecked, costs can exceed £1,400. Getting the unit inspected quickly is the best way to keep costs at the lower end.