Daikin E3-24 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin E3-24 fault code mean?
The E3 fault code on Daikin heat pumps signals that the high-pressure switch (HPS) on the refrigerant circuit has tripped. When refrigerant pressure on the high side of the system climbs beyond the safe threshold, the unit shuts down automatically to protect the compressor and sealed circuit from damage. The '24' suffix seen on some displays typically refers to a unit or system number in a multi-zone installation rather than a separate fault sub-type — the underlying alarm is always the same high-pressure protection event.
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
- Dirty or blocked outdoor heat exchanger coil Common
A coating of dirt, dust, or debris on the outdoor coil restricts heat rejection. The refrigerant cannot shed heat efficiently, so high-side pressure rises until the HPS trips. This is the single most common trigger for E3 on Daikin heat pumps, especially on units that have not been serviced for a year or more.
- Obstructed airflow around the outdoor unit Common
Fencing, garden furniture, overgrown plants, a build-up of leaves, or a snow drift packed around the outdoor unit all choke the airflow the unit needs to reject heat. Even partial blockage in warm weather can push high-side pressure over the limit.
- Outdoor fan motor not running or running slowly Sometimes
If the outdoor fan has failed or is struggling due to a seized bearing or electrical fault, heat cannot be dissipated from the coil and pressure rises rapidly. You may hear the compressor running but no fan noise, or notice that air is barely moving from the top of the unit.
- Refrigerant overcharge Sometimes
If too much refrigerant is in the circuit — often following an incorrect recharge — high-side pressure is elevated under all operating conditions. This points to a previous refrigerant top-up that was not weighed in accurately.
- Defective or faulty high-pressure switch Sometimes
The HPS itself can develop an internal fault or a poor connector contact that causes it to signal a trip even when actual refrigerant pressure is within normal bounds. This is effectively a false alarm from the switch rather than a genuine overpressure condition.
- Clogged refrigerant pipework Rare
A restriction inside the refrigerant pipework — caused by debris, contamination, or a partially blocked expansion valve — can cause pressure to build on the high side. This typically requires pressure measurement and inspection by an F-Gas registered engineer to diagnose.
- Refrigerant leak reducing system balance Rare
A leak that lowers the charge on the low side can sometimes cause unusual pressure distribution and drive high-side readings upward under load. Accompanied by reduced heating output and possible ice formation on the outdoor unit.
How to fix it
- Turn off the heat pump and wait five minutes before restarting DIY safe
Switch the unit off at the controller, then turn off the isolator for the outdoor unit. Wait at least five minutes to allow refrigerant pressures to equalise and the compressor to rest. Restore power and restart normally. If the E3 code returns within a short run time, the underlying cause has not been resolved and further investigation is needed.
- Check the outdoor unit for physical obstructions DIY safe
Walk around the outdoor unit and look for leaves, moss, garden equipment, snow, or anything else within roughly 300–500 mm of the casing. Clear away any debris by hand and make sure the top of the unit — where discharge air exits — is completely unobstructed. Do not use a pressure washer on the coil yourself.
- Inspect the outdoor coil fins for visible dirt or blockage DIY safe
Look through the coil grille for a layer of dust, fluff, or matted debris on the fins. If the fins look visibly dirty or you can see daylight being blocked, this is likely contributing to the fault. A light rinse with a garden hose on a gentle setting from the inside outwards can dislodge surface debris — but deep or chemical cleaning should be left to an engineer.
- Check system water pressure if your heat pump heats water or radiators DIY safe
Look at the pressure gauge on your heating system or buffer vessel. It should typically read between 1.0 and 2.5 bar when cold. If it reads below 1.0 bar, the system may need topping up via the filling loop — consult your installer's handover instructions or the heat pump manual for the correct procedure for your installation.
- Arrange a professional inspection of the outdoor fan and coil heat pump engineer
An MCS-certified engineer will check that the outdoor fan is spinning at the correct speed, inspect the fan motor electrically, and carry out a thorough coil clean using appropriate equipment and cleaning agents. Do not attempt to remove the fan guard or touch the fan blades yourself.
- Have refrigerant pressure and charge verified by an F-Gas registered engineer heat pump engineer
The engineer will connect manifold gauges to check actual high and low side pressures against the expected values for the ambient temperature and refrigerant type (typically R-32 or R-410A on Daikin heat pumps). If the charge is found to be too high or too low, refrigerant will be recovered or added accordingly. This work is legally restricted to F-Gas registered engineers in the UK.
- Have the high-pressure switch and connector contacts tested heat pump engineer
If pressures are found to be within normal limits, the engineer will test the HPS itself for continuity and inspect the connector for corrosion or a loose pin that could cause a spurious trip. A faulty switch is straightforward to replace once confirmed.
- Have the PCB and refrigerant pipework inspected if the fault persists heat pump engineer
Should the steps above not identify the cause, the system control board or a restriction within the refrigerant circuit may be responsible. The engineer may also carry out a leak test on the circuit. Contact an MCS-certified heat pump engineer — and ensure they hold F-Gas registration for any sealed circuit work.
Parts you may need
- High-pressure switch (HPS) · from £45
- Outdoor fan motor · from £180
- Outdoor fan capacitor · from £20
- Refrigerant R-32 (per kg, supply and reclaim) · from £35
- Outdoor unit PCB / control board · 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 reset the Daikin E3 fault code myself?
Yes, you can attempt a reset by switching the unit off at the controller and isolator for five minutes before restarting. However, if the underlying cause has not been addressed the code will return quickly — sometimes within minutes. A successful reset followed by normal, stable operation suggests the trip was triggered by a temporary condition such as a brief airflow obstruction. If the fault keeps coming back, an engineer needs to investigate.
Will a dirty outdoor unit really cause the E3 code?
Yes — it is actually the most common reason for E3 on Daikin heat pumps. The outdoor coil relies on a free flow of air to transfer heat out of the refrigerant. When the coil fins are caked with dirt or airflow is restricted, the refrigerant cannot shed its heat fast enough and high-side pressure climbs until the safety switch trips. Annual servicing that includes a professional coil clean is the most effective way to prevent this fault recurring.
How much does it typically cost to fix a Daikin E3 fault in the UK?
Most E3 repairs fall between £150 and £450 including callout, diagnosis, and the most common fixes such as a coil clean or a high-pressure switch replacement. If the outdoor fan motor has failed, expect costs toward the top of that range or slightly above. More involved repairs — such as a refrigerant leak, a circuit board failure, or in the worst case compressor damage — can run to £600–£2,000 or more, but these are much less frequent causes of E3. If your system is still under warranty, contact Daikin to authorise the repair before booking an engineer.
Does fixing the Daikin E3 fault require an F-Gas engineer?
It depends on what caused it. Clearing debris, checking system pressure, and resetting the unit are tasks any homeowner can do safely. However, if the refrigerant charge needs checking, adjusting, or replenishing, or if there is a leak in the sealed circuit, the work is legally restricted to engineers holding a valid UK F-Gas qualification. Your MCS-certified heat pump engineer should hold the appropriate F-Gas certificate; if in doubt, ask before booking.