Daikin E8-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin E8-00 fault code mean?
The E8-00 fault code means the outdoor unit's inverter has detected an abnormally high current draw from the compressor circuit and has shut the system down as a protective measure. The inverter — the electronics responsible for controlling compressor speed — monitors current continuously, and when the reading exceeds safe limits, it triggers this lockout to prevent further damage to expensive components. This is strictly an outdoor unit fault and should be treated seriously: repeated forced restarts can turn a manageable repair into a full compressor replacement.
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
- Faulty inverter PCB or power module (IPM) Common
The Intelligent Power Module or main inverter PCB can fail due to age, power surges, or moisture ingress, causing it to report an overcurrent condition even when the compressor itself is healthy. This is one of the most common confirmed causes once electrical diagnosis is completed.
- Failed capacitor or power transistor on the inverter board Common
The main circuit capacitors or power transistors on the inverter assembly degrade over time. A capacitor losing its capacitance or a transistor breaking down can cause excessive current spikes that trigger E8-00 before any mechanical failure has actually occurred.
- Poor or unstable mains supply Sometimes
Under-voltage, loose terminal connections, or an imbalanced supply reaching the outdoor unit can cause the inverter to draw higher-than-normal current as it struggles to maintain compressor operation. This is worth ruling out early as it is a relatively simple check for an engineer.
- Compressor winding breakdown or mechanical seizure Sometimes
If the compressor windings have degraded — detectable via insulation resistance (Megger) testing — or the compressor has partially or fully seized mechanically, the inverter will be forced to supply excessive current to try to drive it. This is the most costly outcome and should only be concluded after all electrical components have been tested and cleared.
- Wiring fault between inverter and compressor Rare
Damaged, loose, or corroded wiring on the compressor terminal block or inverter output connections can create resistance that the inverter interprets as an overcurrent condition. Less common but worth inspecting as part of a systematic diagnosis.
How to fix it
- Switch off at the isolator and wait at least five minutes before restarting DIY safe
The inverter capacitors inside the outdoor unit take several minutes to fully discharge after power is removed. Switch off the dedicated outdoor unit isolator, wait a full five minutes, then restore power. Allow two minutes for the system to initialise before attempting to run it. This one reset is appropriate; if E8-00 returns promptly, do not reset again — repeated restarts under a genuine overcurrent fault can cause escalating damage.
- Check for any tripped MCB on your consumer unit related to the heat pump DIY safe
Go to your consumer unit (fuse board) and check whether the circuit breaker for the heat pump has tripped. If it has tripped and resets without immediately tripping again, this may indicate an intermittent supply issue worth reporting to your engineer. If it trips again on reset, leave it off and call an engineer.
- Do not attempt further resets if the fault returns DIY safe
An E8-00 that reappears within the same operating cycle is a confirmed electrical fault. Continuing to run the unit risks converting a repairable inverter PCB fault into a compressor replacement. Leave the unit off and arrange professional diagnosis.
- Engineer: check the mains supply, terminal connections and supply voltage heat pump engineer
An MCS-certified engineer should measure incoming supply voltage and inspect all terminal connections at the outdoor unit supply and inverter input. Under-voltage or loose terminals can cause the inverter to overcurrent and must be ruled out before any component replacement is considered.
- Engineer: test the inverter PCB, power module (IPM), capacitors and power transistors heat pump engineer
Using appropriate test equipment, the engineer should assess the main circuit capacitors for capacitance loss and the power transistors and IPM for breakdown. These components fail more frequently than the compressor itself and are the starting point for diagnosis.
- Engineer: carry out Megger insulation resistance testing on the compressor windings heat pump engineer
Only after the inverter electronics have been assessed should compressor winding resistance be measured. Low or zero insulation resistance indicates winding breakdown and confirms compressor-side failure. This is a critical step that prevents unnecessary compressor replacement if the fault lies elsewhere.
- Engineer: replace the identified faulty component and retest heat pump engineer
Depending on findings, the repair will typically be an inverter PCB or power module replacement, a capacitor or transistor swap, or — in the worst case — a compressor replacement. Any work on the refrigerant circuit requires an F-Gas registered engineer. After replacement, the engineer should run the unit through a full operating cycle and confirm E8-00 does not return.
- If diagnosis confirms compressor failure, weigh repair cost against unit age and condition DIY safe
Compressor replacement is a significant cost. Ask your engineer for a written quote and consider the unit's age, remaining warranty, and whether an annual service history has been maintained. Daikin's residential warranty typically covers manufacturer defects for three years provided annual servicing by a qualified engineer has been carried out.
Parts you may need
- Daikin inverter PCB (outdoor unit main board) · from £380
- Intelligent Power Module (IPM / power transistor module) · from £220
- Inverter electrolytic capacitor set · from £65
- Compressor wiring harness and terminal kit · from £45
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 £350–£900, depending on the underlying cause.
Frequently asked questions
Can I keep resetting the heat pump when E8-00 appears?
One carefully managed reset — after a full five-minute isolation — is reasonable to rule out a transient glitch. Beyond that, no. E8-00 indicates the inverter is detecting unsafe current levels, and forcing the unit to run repeatedly under these conditions can turn a repairable PCB or power module fault into a full compressor failure, potentially adding over a thousand pounds to the repair bill. Reset once; if the fault returns, switch off and call an engineer.
Does E8-00 always mean the compressor needs replacing?
Not at all, and a good engineer will not jump to that conclusion. The E8-00 code tells you there is an overcurrent condition in the inverter-to-compressor circuit — but that overcurrent can originate from a failed power module, a degraded capacitor, a faulty inverter PCB, or a poor mains supply. Only after those components are tested and cleared should compressor winding failure be considered. In many cases, an inverter PCB or power module replacement resolves E8-00 completely.
How much does it typically cost to fix E8-00 on a Daikin heat pump in the UK?
Most E8-00 repairs in the UK fall in the range of £350–£900, covering engineer diagnosis time and an inverter PCB or power module replacement including parts and labour. If the compressor itself has failed, costs rise substantially — a compressor replacement on a typical Daikin Altherma unit can exceed £1,400–£2,000 or more depending on model size and system complexity. This is why prompt, systematic diagnosis matters: catching it at the inverter-board stage is considerably cheaper than letting the fault progress.
Does refrigerant need to be handled to fix E8-00?
In most cases, no — inverter PCB and power module repairs do not involve the refrigerant (sealed) circuit. However, if the diagnosis ultimately confirms compressor replacement is required, the refrigerant will need to be recovered and later recharged, and that work must be carried out by an F-Gas registered engineer. Always confirm your engineer holds the appropriate F-Gas qualification before any sealed-circuit work begins.