A Mitsubishi Electric Ecodan error code is a short letter and number pair, such as L9 or E6, that the system shows when it spots a fault. On Ecodan systems with the FTC6 controller, the main remote controller displays the code along with which unit raised it. Most codes point to the water circuit, a sensor or a lost connection.
Some have simple causes you can check yourself, like a remote with a flat battery or an outdoor unit that has been switched off. Others need an engineer with the right tools and qualifications. Codes beginning U, F or A come from the outdoor unit and always need a professional.
If a code keeps coming back, or you are not sure what it means, we can book an Ecodan repair with an F-Gas certified engineer. For other makes, our heat pump error codes guide covers them by brand.
Safety first: never open the indoor or outdoor unit covers, and isolate the power before clearing anything from around the outdoor unit.
Please read first: this guide is here to help you understand what your Mitsubishi Electric Ecodan heat pump is telling you. Every effort has been made to keep the information accurate, but manufacturers update their manuals and codes can differ between models and software versions, so always check the official Mitsubishi Electric Ecodan manual for changes before acting on anything here. Do not attempt anything that could be dangerous, and avoid any work that could void your warranty. If in doubt, call a qualified heat pump engineer.
If your Mitsubishi Ecodan heat pump is not showing a code, or you want to rule out the basics first, our guide to air source heat pump problems walks through the general checks and matches common faults to error codes across every major brand.
Is it safe to fix a Mitsubishi Ecodan fault yourself?
Only basic checks are safe unless you are a competent heating engineer. Reading the pressure gauge, changing remote batteries, checking the isolator and clearing debris from outside the unit are fine.
Never remove covers to test thermistors, cables or circuit boards. Those checks mean working near mains voltage, and the FTC6 manual's own actions for most codes are written for installers, not homeowners.
Anything involving refrigerant, including checking the charge, is legally restricted to F-Gas certified engineers. Unqualified work inside the unit can also affect your manufacturer warranty, so check your paperwork before going further than the steps below.
Which Ecodan error codes can you check yourself?
A homeowner can safely check the Ecodan codes linked to power, remote controls and water pressure. The rest need an engineer.
| Code | What it means | Safe homeowner check | Stop and call an engineer if |
|---|---|---|---|
| J1 to J8 | Wireless remote has lost contact with its receiver | Fit fresh batteries and use the remote closer to the receiver | It still fails with new batteries |
| E6 to EF, E9 | Indoor controller and outdoor unit are not talking | Check the outdoor unit's isolator and breaker are on | Both are on and the code stays |
| E0 to E5 | Main remote controller has lost contact with the FTC | Switch the system off and on once | It returns after the restart |
| L3, L6, L9 | Water circuit overheating, freeze protection or low flow | Read the pressure gauge and check any valves you closed are open again. Top up only if you have a filling loop and your manual allows it | Pressure is normal and the code returns |
| LE | Boiler operation error on hybrid systems | Look at the boiler for its own fault or lockout | The boiler shows a fault too |
A blank controller screen has no code, but it often means no power. Check the breaker at your consumer unit before calling.
What are the most common Ecodan error codes?
The Ecodan codes we see most are freeze protection, low flow, overheating, high pressure, sensor and communication faults. Mitsubishi's FTC6 manual does not rank codes by how often they appear. Causes labelled general engineering knowledge come from our experience, not the manual.
L6 and P6: freeze protection
L6 means the circulating water got cold enough to trigger freeze protection. P6 is anti-freeze protection for the plate heat exchanger, where heat passes from refrigerant to water. The manual's checks for both are leaks, a blocked strainer and the circulation pump, with the refrigerant charge added for P6.
As general engineering knowledge, low flow on a cold night is the usual trigger. Read our advice on running a heat pump in cold weather, then call us if it repeats, as P6 may need an F-Gas engineer.
L9 and LP: low flow
L9 means the flow sensor or flow switch has detected low flow in the primary circuit. LP means the flow rate is outside the range the outdoor unit needs. The manual points to leaks, the strainer and the pump for L9, and to the flow rate settings for LP.
As general engineering knowledge, a clogged strainer, trapped air, scale or sludge are the usual causes. An engineer will clean the strainer and test the pump, and a heavily sludged system may need a heat pump powerflush.
L3: water overheating
L3 means the circulating water has overheated, which the manual says may come from reduced flow. It can also appear while the primary circuit is being filled, in which case the installer finishes filling and resets it.
As general engineering knowledge, sludge, an air lock or closed zone valves are common causes. If it appears out of the blue, book an engineer.
LB: high pressure protection
LB means the refrigerant pressure has gone too high. The manual lists reduced flow in the heating circuit, a clogged plate heat exchanger or an outdoor unit fault.
Scale and debris in the plate heat exchanger are typical underlying causes, from general engineering knowledge. This needs an engineer, and an F-Gas engineer if the outdoor unit is at fault.
L5, L8, P1 and P2: sensor faults
L5 means one of the indoor water temperature sensors (thermistors) has failed. P1 and P2 are the room and refrigerant liquid sensors, and L8 is a heating operation error that the manual links to a dislodged sensor. The engineer's fix is to test the sensor's resistance or refit it.
Water in a connector or a damaged cable is a common cause, as general engineering knowledge. There is no safe homeowner check here.
E6 to EF and E9: outdoor unit communication
These mean the indoor controller (FTC) and the outdoor unit have lost contact. E9 means the outdoor unit is getting no signal from indoors. The manual's first check is that the outdoor unit has not been switched off.
Check the isolator and breaker. If both are on, an engineer needs to test the cable between the two units.
E0 to E5 and J codes: controller communication
E0 to E5 mean the main remote controller has lost contact with the FTC. J1 to J8 are between a wireless remote and its receiver, and the manual's first check is the battery. J0 and J9 are wiring faults between control boards.
Change the remote batteries first. For E codes or J0 and J9, book an engineer to check the cables.
L4: hot water tank overheating
L4 means the hot water cylinder has gone over its safe temperature. The manual's check is the immersion heater and its contactor (the switch that powers it).
A stuck contactor or a failed thermostat is a likely cause, from general engineering knowledge. Leave this to an engineer, as it involves mains-powered heater controls.
U, F and A codes: outdoor unit faults
Any code beginning U, F or A comes from the outdoor unit. The FTC6 manual does not list these and refers engineers to the service manual for your outdoor model.
Note the full code and your outdoor unit model, then book an engineer. Many of these involve the refrigerant circuit or compressor electronics.
Which error code might you see in common situations?
What was happening when the code appeared is often the best clue. These are the Ecodan codes most likely in everyday situations, with the first thing to check.
| Scenario | Codes you may see on an Ecodan | First check |
|---|---|---|
| Cold snap, outdoor unit iced up | L6, P6, or an outdoor U, F or A code | Power is on and snow is clear of the unit. See our tips for a frozen outside unit |
| Losing pressure or low pressure | L9, L3, LA | Gauge reading, and whether the relief valve pipe outside is dripping |
| Radiators lukewarm | L9, LP, L3, LB | Timer, holiday or prohibit mode on the controller, then valves |
| No hot water | L4, LJ | Breaker for the immersion heater, and hot water timer settings |
| After a power cut | E0 to E5, E6 to EF, E9 | Wait: "Please Wait" for up to 6 minutes is normal |
| Unit noisy or fan not spinning | Outdoor U, F or A code | Debris or ice around the fan, with power isolated first |
| After a service or filter clean | L3, L9, L8, LL | Pressure restored and every valve reopened |
A few things are normal and not faults, according to the manual. The pump may run briefly to stop it seizing, the 3-way valve can click as it moves, and the system returns to hot water mode after a power cut.
How do you reset a Mitsubishi Ecodan heat pump?
On an FTC6 Ecodan, you clear the current error from the main remote controller by pressing F4 (RESET) and then F3 (Yes). The manual also says switching the system off will cancel error codes.
- Write down the code, or photograph the screen.
- Press F4 (RESET) on the main remote controller.
- Press F3 (Yes) to confirm.
- Give the system a few minutes to restart. "Please Wait" can show for up to 6 minutes.
If the buttons do nothing, switching the system off and on again is the fallback. Do not keep resetting a code that returns. Each restart puts the compressor through another start, and it hides the pattern an engineer needs to see.
If the heating still will not run after a single reset, our guide to a heat pump not heating covers other causes.
Ecodan error code list
This list covers every code in the self-check table of the Ecodan FTC6 installation manual. Outdoor unit codes are listed by their first letter only, so check the service manual for your outdoor model.
| Code | Meaning | Who should fix |
|---|---|---|
| L3 | Circulating water overheat protection | Homeowner check, then engineer |
| L4 | Hot water cylinder overheat protection | Engineer |
| L5 | Indoor water temperature sensor failure | Engineer |
| L6 | Circulating water freeze protection | Homeowner check, then engineer |
| L8 | Heating operation error | Engineer |
| L9 | Low primary circuit flow rate | Homeowner check, then engineer |
| LA, LF | Pressure sensor or flow sensor failure | Engineer |
| LB | High pressure protection | Engineer, F-Gas engineer if outdoor unit |
| LC, LH | Boiler circuit overheat or freeze protection (hybrid) | Engineer |
| LD | Boiler temperature sensor failure (hybrid) | Engineer |
| LE | Boiler operation error (hybrid) | Homeowner check, then engineer |
| LJ | Hot water operation error (external plate heat exchanger type) | Engineer |
| LL | DIP switch setting error on the FTC board | Engineer |
| LP | Flow rate outside the outdoor unit's range | Engineer |
| P1, P2 | Room or refrigerant liquid sensor failure | Engineer |
| P6 | Plate heat exchanger anti-freeze protection | F-Gas engineer |
| J0, J9 | Wireless receiver or main-to-sub FTC communication failure | Engineer |
| J1 to J8 | Wireless remote to receiver communication failure | Homeowner check, then engineer |
| E0 to E5 | Main remote controller to FTC communication failure | Homeowner check, then engineer |
| E6 to EF, E9 | FTC to outdoor unit communication failure | Homeowner check, then engineer |
| EE | FTC and outdoor unit combination error | Engineer |
| U, F or A codes | Outdoor unit failure | F-Gas engineer |
Where can you find the official Mitsubishi Electric Ecodan manual?
Mitsubishi Electric publishes its Ecodan manuals free in its UK document library. The FTC6 installation manual holds the full self-check code table used in this guide, while outdoor unit codes are in the service manual for your outdoor model.
- Ecodan FTC6 PAC-IF07 installation manual BH79D843H06 (PDF)
- Ecodan FTC6 installation manual, online viewer
- Mitsubishi Electric UK library: Ecodan controls installation manuals
Need help with a Mitsubishi Ecodan fault?
We repair Mitsubishi Electric heat pumps across the UK, including Ecodan systems of every age. Our engineers are F-Gas certified, so they can deal with the outdoor unit and refrigerant circuit as well as the water side, and our repairs come with a 12-month guarantee.
Every visit starts with proper fault diagnosis, and we quote for the repair before any work begins. If you have no heating or hot water, our emergency heat pump repair service aims for same-day visits where possible. Otherwise, book a standard heat pump repair.
Many Ecodan codes, especially L9, L3 and LB, trace back to a dirty strainer or a scaled heat exchanger. Annual heat pump servicing catches these early, and our cover plans spread the cost.
Call 0333 041 5130 or contact us online.
Frequently asked questions
Does an Ecodan error code void my warranty?
No, a code by itself does not affect your warranty. Problems tend to come from unqualified repairs inside the unit or gaps in the service history, as manufacturer warranties usually depend on both. Keep your service records safe and use a certified engineer.
Can I see Ecodan error codes on my phone?
If your system is connected to Mitsubishi Electric's online controls, faults may also show as alerts there. The main remote controller is still the most reliable place to read the full code and which unit raised it. Our Mitsubishi Ecodan review looks at the range in more detail.
Does an outdoor unit code mean the compressor has failed?
Not necessarily. U, F and A codes cover a range of outdoor faults, and many turn out to be sensors, wiring or the power supply. Our guide to heat pump compressor problems explains the signs of a genuine compressor failure.
Why is my Ecodan losing pressure with no error code?
The manual links water from the pressure relief valve to two faults. A constant drip suggests a damaged valve, while an occasional one points to a low or failed expansion vessel. See our guide to a heat pump losing pressure for what to check next.
Why is my Ecodan circulation pump noisy?
A noisy pump usually has air trapped in it, according to the manual. An engineer will bleed it through the air vents and bring the primary circuit back up to pressure. If the noise is coming from outside instead, read our guide to a heat pump making noise.
