Daikin E2-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin E2-00 fault code mean?
The E2-00 code means the Daikin Altherma outdoor unit's main PCB has detected an unwanted electrical current flowing to earth somewhere within the outdoor unit. As a protective measure, the heat pump shuts itself down immediately. This is a genuine electrical safety fault — not a nuisance trip — and the system will not restart normally until the underlying cause has been identified and rectified 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
- Compressor winding insulation failure Common
Over time — or due to moisture ingress, overheating, or refrigerant contamination — the insulation on the compressor's internal windings can break down, allowing current to leak to earth. The outdoor unit PCB detects this instantly and locks the system out. This is the single most common root cause of E2-00 and unfortunately one of the more costly repairs.
- Faulty or incorrectly wired leakage current sensor Sometimes
The outdoor unit contains a dedicated current sensor (often referenced as T1A in Daikin service documentation) that monitors for earth leakage. If its wiring connector (e.g. X101A) is loose, disconnected, corroded, or the sensor itself has failed, the PCB may interpret this as a genuine earth fault and raise E2-00 even when no actual leakage exists. This is a less expensive fix than a compressor but still requires a qualified engineer to diagnose.
- Defective outdoor unit main PCB Sometimes
If the leakage detection circuit on the PCB itself develops a fault — due to component ageing, moisture ingress, or electrical surge — it can trigger a false E2-00 alarm. The rest of the electrical system may be perfectly healthy, but the board incorrectly reports an earth fault. PCB failure is less common than the above two causes but should be considered once the compressor and sensor have been ruled out.
- Moisture ingress into outdoor unit wiring or terminals Rare
Water finding its way into the outdoor unit's wiring loom, terminal blocks, or electrical enclosure — for example after prolonged heavy rain or a pressure-washing incident — can temporarily reduce insulation resistance to earth and trigger E2-00. In some cases the fault clears once the unit dries out thoroughly, but persistent moisture damage will require attention.
How to fix it
- Switch off the heat pump at the indoor controller and check for any tripped MCB at your consumer unit DIY safe
Before anything else, go to your consumer unit (fuse board) and check whether the circuit breaker for the heat pump has tripped. If it has, this supports the presence of a genuine earth fault — do not simply reset it and leave the system running. Note it down and report this to your engineer. If no MCB has tripped, switch the heat pump off from the indoor controller or thermostat.
- Check the outdoor unit for obvious external issues — debris, standing water, or signs of physical damage DIY safe
Walk around the outdoor unit and look for anything unusual: pooled water around the base, flood damage, evidence of pest activity, or visible damage to the casing or wiring entry points. Clear any leaves, debris, or vegetation that may have accumulated directly against the unit. Do not open any panels or touch any wiring inside the unit.
- Wait 10–15 minutes, then attempt a single restart from the indoor controller DIY safe
In rare cases — for example where moisture has caused a temporary drop in insulation resistance — a brief power-off period and restart may allow the system to run again. However, if E2-00 returns immediately or within a short time, do not keep cycling the power. Repeated restart attempts on a genuine earth fault can cause further damage. If the fault clears and the system runs normally for more than a day, still arrange an engineer inspection to rule out an intermittent insulation problem.
- An MCS-certified engineer should test insulation resistance on the compressor windings using a megger heat pump engineer
This is the key diagnostic step. The engineer will use an insulation resistance tester (megger) to measure the resistance between each compressor winding and earth. A healthy compressor will show very high resistance (typically several megohms); a failing compressor will show a low or zero reading, confirming the earth fault origin. This test must only be carried out by a qualified engineer with the unit's electrical supply fully isolated.
- An engineer should inspect and test the leakage current sensor and its wiring connections heat pump engineer
The engineer will check the current sensor connector (X101A) and associated wiring for looseness, corrosion, fraying, or incorrect routing. They will use a multimeter to verify continuity and correct resistance values. If a faulty or displaced connector is the culprit, reconnection or sensor replacement is a relatively straightforward and lower-cost repair compared to a compressor replacement.
- An engineer should assess the outdoor unit main PCB if the compressor and sensor both test healthy heat pump engineer
If insulation resistance is good and the sensor wiring is intact, the PCB's own leakage detection circuit may be generating a false alarm. The engineer will carry out further electrical testing of the board and, if confirmed faulty, arrange a replacement outdoor unit PCB. This typically needs to be sourced from Daikin or a specialist supplier.
- If your unit is under warranty, contact Daikin UK before booking an independent engineer DIY safe
Daikin's warranty terms generally require faults to be reported to Daikin UK directly so the repair can be authorised and covered. Using a non-approved engineer for a warranty repair can invalidate the claim. Contact Daikin UK's customer support line or your installing company in the first instance. Note that most Daikin warranties also require evidence of annual servicing — if you have missed a service, check the small print before proceeding.
- Call an MCS-certified heat pump engineer to carry out diagnosis and repair heat pump engineer
E2-00 is an electrical safety fault that cannot be safely diagnosed or repaired by a homeowner. The repair will require specialist electrical testing equipment and, if refrigerant system components are involved, an F-Gas registered engineer. Use the MCS installer database (mcscertified.com) or contact Daikin UK to find an approved service partner in your area.
Parts you may need
- Outdoor unit main PCB (Daikin Altherma) · from £280
- Leakage current sensor / earth leakage CT sensor · from £85
- Wiring loom connector kit (X101A / T1A) · from £25
- Compressor (Daikin Altherma — model dependent) · from £950
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–£650, depending on the underlying cause.
Frequently asked questions
Is E2-00 dangerous — should I stop using the heat pump immediately?
Yes, you should leave the heat pump switched off until an engineer has investigated. E2-00 indicates the system has detected current leaking to earth, which is a genuine electrical safety concern. The unit's protection circuits have already shut it down for this reason. Repeatedly restarting the system and ignoring the fault risks causing further damage to the compressor or electrical components, and in a worst-case scenario could pose a shock or fire hazard.
Could E2-00 be a false alarm, or does it always mean the compressor is failing?
Not every E2-00 points to a failed compressor. A loose or corroded connector on the leakage current sensor is a fairly common cause and is a much cheaper fix — typically £180–£350 all in. A defective outdoor PCB generating a false reading is another possibility. Your engineer will megger-test the compressor windings first; if insulation resistance is healthy, attention shifts to the sensor and PCB. Only once those are ruled out is compressor failure confirmed.
How much does it cost to replace the compressor on a Daikin Altherma if E2-00 is caused by insulation failure?
Compressor replacement sits outside the typical repair range and is one of the more significant heat pump repairs. Parts alone for a Daikin Altherma compressor generally start around £900–£1,200 depending on the model, with labour and refrigerant recovery/recharge adding a further £400–£600 or more, bringing total costs to roughly £1,500–£2,000+. If your unit is still under warranty or you have a heat pump service plan, check coverage before committing to any repair costs — this is exactly the type of failure those products are designed for.
Will my Daikin warranty cover an E2-00 repair?
It may do, provided certain conditions are met. Daikin's standard warranty typically requires the fault to be reported directly to Daikin UK before an engineer visits, so an approved Daikin service partner can carry out the work and the repair can be authorised. Crucially, most Daikin warranties also require evidence of annual servicing as a condition of cover — if annual services have not been carried out and documented, Daikin may decline the warranty claim. Check your warranty documentation and call Daikin UK's support line as a first step.