Daikin E5-00 Fault Code: Causes, Fixes & Repair Costs
What does the Daikin E5-00 fault code mean?
The E5-00 fault code on a Daikin heat pump indicates that the system's overload protector (OL) has triggered a protective shutdown to prevent compressor damage. In plain terms, the unit has detected that the compressor is running under conditions that are either too hot, drawing too much current, or both — and has locked out to stop things getting worse. The '-00' sub-code identifies this as the primary fault instance on that circuit. E5 faults span the full Daikin range, from domestic Altherma splits to larger multi-zone systems, and should always be taken seriously because continuing to run a compressor under overload conditions can turn a modest repair into a very expensive one.
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
- Low or leaking refrigerant Common
A refrigerant shortage is the single most frequent trigger for E5. When refrigerant levels drop — almost always due to a leak rather than normal consumption — the compressor has to work harder to move heat, raising its temperature and current draw until the overload protector trips. Under UK F-Gas Regulations 2015, any engineer who simply tops up refrigerant without first locating and repairing the leak is acting unlawfully.
- Dirty or obstructed outdoor heat exchanger coil Common
A heat exchanger caked in dust, cottonwood seeds, or compacted debris cannot transfer heat efficiently. The compressor then has to run harder and hotter to compensate, eventually tripping the OL protector. This is particularly common if the unit has not had an annual service.
- Blocked or restricted refrigerant circuit Sometimes
A partial blockage anywhere in the refrigerant piping — including a partially closed service valve left that way after previous work, a failing expansion valve, or a clogged strainer — raises the load on the compressor significantly and can cause overheating.
- Faulty discharge pipe thermistor or loose connection Sometimes
The discharge pipe thermistor monitors compressor outlet temperature. If this sensor has a loose connector or a drifting resistance value, it can send false high-temperature readings to the outdoor PCB, triggering an E5 fault even when the compressor itself is healthy.
- Faulty overload protector (OL) or wiring Sometimes
The OL protector itself can fail or develop a poor connection at its wiring harness (connector S40 on many Daikin models). A faulty OL may trip at normal operating temperatures, causing nuisance E5 faults that reappear after reset.
- Outdoor PCB fault Sometimes
A malfunctioning outdoor PCB can misread sensor inputs or send incorrect drive signals to the compressor, effectively causing it to overload. This is usually only identified after sensors and refrigerant circuit checks have been ruled out.
- Compressor winding failure Rare
A degraded compressor motor winding draws excessive current from the moment it tries to start, immediately triggering the OL. This is one of the more serious outcomes and typically means compressor replacement is required.
- Mains supply voltage issues Rare
Significant voltage fluctuations or a supply that falls outside the unit's rated tolerance can cause the compressor to draw abnormal current. Worth noting if other appliances on the same supply are also misbehaving.
How to fix it
- Switch the unit off and allow a 10-minute cooldown DIY safe
Turn the heat pump off at its controller and, if accessible, at the outdoor unit isolator. Wait at least 10 minutes to give the compressor time to cool before attempting a restart. Only try this once or twice — if E5 returns after a single reset, stop and arrange a service call. Repeatedly forcing restarts on a genuine compressor overload fault causes cumulative damage.
- Clear the area around the outdoor unit DIY safe
Walk around the outdoor unit and remove any leaves, debris, snow, or objects within at least 30 cm on all sides and above the fan outlet. Restricted airflow directly worsens overheating. Do not hose the coil yourself unless the unit is fully isolated; leave coil cleaning to an engineer.
- Check the main consumer unit for any tripped MCBs DIY safe
If the outdoor unit has lost power entirely, check your consumer unit (fuse board) for a tripped breaker labelled for the heat pump. Reset it once if tripped. If it trips again immediately, do not reset it a second time — this indicates a wiring or electrical fault that needs professional attention.
- Restart the unit and monitor DIY safe
Once the cooldown period has passed and airflow is clear, switch the unit back on from the controller. If the system runs normally without the E5 returning within the first heating cycle, continue to monitor over the next 24 hours. If E5 returns at any point, proceed to booking an engineer.
- Engineer: check the discharge pipe thermistor and its wiring connector heat pump engineer
An MCS-certified engineer should begin diagnostics at the discharge pipe thermistor. A loose connector at this sensor is a relatively simple fix. If the connector is secure, measuring the thermistor's resistance against the expected value at a known temperature will confirm whether the sensor has drifted and needs replacement.
- Engineer: inspect the overload protector (OL) and connector S40 heat pump engineer
The engineer should verify that the OL protector is operating within its correct trip range and that its wiring harness and connector (S40 on most Daikin outdoor units) are free from corrosion, damage, or looseness. A faulty OL can be replaced independently of the compressor if the compressor itself is healthy.
- Engineer: check expansion valve (EV) coil resistance and refrigerant circuit heat pump engineer
The EV coil should be tested for correct resistance. The engineer should also check for any closed service valves, inspect refrigerant pressures, and carry out leak detection on the refrigerant circuit. Any confirmed leak must be located and repaired before refrigerant is added — this is a legal requirement under UK F-Gas Regulations 2015, and this work must be carried out by an F-Gas registered engineer.
- Engineer: test the outdoor PCB and compressor windings heat pump engineer
If refrigerant circuit and sensor checks come back normal, the outdoor PCB should be tested for correct signal output. Compressor winding resistance should also be measured to determine whether the motor has degraded. A failed compressor or PCB will need to be replaced by a qualified engineer.
- If the fault cannot be resolved by sensor or refrigerant repair, arrange specialist engineer attendance heat pump engineer
Contact an MCS-certified heat pump engineer for a full diagnostic. Any work involving the refrigerant (sealed) circuit or the compressor must be carried out by an F-Gas registered engineer. Do not continue operating the heat pump while E5 is active — doing so risks converting a repairable fault into a full compressor failure.
Parts you may need
- Discharge pipe thermistor (Daikin outdoor unit) · from £35
- Overload protector (OL) · from £45
- Expansion valve (EV) coil · from £60
- Outdoor PCB (model-specific) · from £320
- Compressor (model-specific, supply only) · from £850
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 just reset the E5-00 fault and carry on using my Daikin heat pump?
A single reset after a 10-minute cooldown is reasonable — occasionally a brief abnormal operating condition can trigger the OL without indicating a deeper problem. However, if E5 returns after one reset, you should stop using the unit and book an engineer. Running the heat pump repeatedly through an active overload fault risks turning a relatively affordable repair (a thermistor or refrigerant regas) into a full compressor replacement, which can cost £1,400 or more on a small system.
Does E5-00 mean my refrigerant has leaked out?
A refrigerant leak is the most common cause of E5-00, but it is not the only one. Sensor faults, a dirty heat exchanger, or a failing compressor can all produce the same code. That said, heat pumps do not consume refrigerant under normal operation — if an engineer tells you the system simply needs a top-up, ask them to confirm they have located and repaired the source of the loss first. Under UK F-Gas Regulations 2015, adding refrigerant to a leaking system without repairing the leak is unlawful.
How much does it cost to fix a Daikin E5-00 fault in the UK?
Most E5-00 repairs fall in the £180–£600 range. A thermistor or overload protector swap with labour typically costs £180–£350. A refrigerant leak repair and regas usually runs £350–£600. PCB replacement sits higher, typically £450–£900 including parts and labour. Compressor replacement is a significantly larger job — expect upwards of £1,400 for a domestic split system, and considerably more for larger multi-zone or ground-source systems. These figures are best treated as a guide; an engineer's diagnostic visit will confirm what is actually needed.
How can I prevent E5-00 from coming back?
Routine maintenance is the most effective prevention. Clean or check indoor filters every four to six weeks during heavy use, ensure the outdoor unit always has at least 30 cm of clearance on all sides, and arrange a professional service (including outdoor coil cleaning and refrigerant pressure checks) every 12 months. MCS-certified heat pump engineers will also check electrical connections and sensor readings during a service, catching early signs of component wear before they trigger a lockout fault.