Mitsubishi Ecodan heat pumps are well-known for their energy efficiency and reliability, making them a popular choice of heat pump in the UK. However, like any advanced heating solution, they can encounter issues from time to time, which are indicated by specific error or fault codes. If you are reading this article then you are likely already the proud owner of an Ecodan, but you might find our review of the Ecodan interesting if you would like a different opinion on the choice of unit.
In this guide, we’ll walk you through the most common Mitsubishi Ecodan fault codes, what each one means, and give you some step-by-step troubleshooting advice. Whether you're dealing with a water circulation issue, thermistor failure, or communication error, this article will help you quickly identify the problem. You will note that the resolution is not always straightforward, so some of you might have the experience and knowhow to resolve some of the issues yourself, while in other cases it might be best to seek professional help.
What Are Mitsubishi Ecodan Error Messages?
Mitsubishi Ecodan heat pumps use diagnostic error codes to indicate faults and issues with the unit or system. These codes are displayed on the controller panel, helping homeowners and technicians pinpoint the root cause of the issues quickly and efficiently.
Some fault codes can be resolved with simple troubleshooting, while others may require professional servicing.
Common Mitsubishi Ecodan Fault Codes Explained
Here are some of the most frequently encountered Mitsubishi Ecodan fault codes, their meanings, and suggested actions:
F3 - Low Pressure Switch Failure: Check the connection on the board and verify the continuity of the switch.
F5 - High Pressure Switch Failure: Inspect the connection on the board and ensure proper switch operation.
L3 - Circulation Water Temperature Overheat Protection: Check for water leakage, strainer blockage, and ensure the circulation pump is functioning correctly.
L9 - Low Primary Circuit Flow Rate Detected: Inspect for water leakage, strainer blockage, and replace the flow switch if necessary.
U1 - High Pressure Fault: Check water flow rates and ensure no blockages.
U6 - Inverter/Compressor Overcurrent: Perform diagnostic tests on the inverter and compressor.
E0 - Transmitting Error (PAR-W21): Verify and correct refrigerant address settings on SW1.
E6 - Indoor/Outdoor Communication Error: Ensure proper power-up sequence and inspect communication lines.
For a full list of fault codes, meanings, and actions, refer to the detailed table below.
Fault Code
Description
Possible Causes
Suggested Actions
F3
Low Pressure Switch Failure
Connection issues on the board or continuity problems with the switch.
Check the connection on the board and verify the continuity of the switch.
F5
High Pressure Switch Failure
Connection issues on the board or continuity problems with the switch.
Check the connection on the board and verify the continuity of the switch.
F9
Both Pressure Switch Contacts Open Simultaneously
Simultaneous activation of both pressure switches.
Inspect both pressure switches for faults and ensure they are operating correctly.
EA
Mis-wiring Between FTC and Ecodan
Incorrect wiring between the FTC and the Ecodan unit.
Verify connections S1, S2, S3; check voltages and communication lines.
EB
Mis-wiring Between FTC and Ecodan
Incorrect wiring between the FTC and the Ecodan unit.
Verify connections S1, S2, S3; check voltages and communication lines.
EC
Unit Cannot Complete Start-Up Process
Communication fault or system startup sequence error.
Inspect communication lines, verify power sequence, and reset the system.
U1
High Pressure Fault
Water flow rate too low, restricted pipes, or blockages.
Check water flow rates, clear blockages, and ensure strainer is clean.
U2
High Compressor Discharge Temperature
Low refrigerant levels, dirty condenser, or poor airflow.
Inspect refrigerant levels, clean condenser, and ensure proper airflow.
U3
Discharge Thermistor Problem
Open or short circuit in TH4 thermistor.
Check TH4 thermistor wiring and replace if necessary.
U4
Open or Closed Circuit Thermistors
Issues with thermistors TH3, TH32, TH33, TH6, TH7, TH8.
Inspect thermistor connections and replace faulty units.
U5
Inverter Heat Sink Overheat Protection
Poor airflow or faulty fan motor.
Ensure airflow is clear, inspect fan motor, and replace if faulty.
U6
Inverter/Compressor Overcurrent
Fault in inverter or compressor operation.
Run inverter diagnostics and inspect compressor operation.
U8
Fan Motor Problem
Disconnected motor, obstructions, or faulty control board.
Check fan motor connections, clear obstructions, and inspect the control board.
U9
Over Voltage or Under Voltage
Loose connections at CN2 or CN5, or unstable power supply.
Secure CN2 and CN5 connections; monitor and stabilize mains voltage.
UD
Overheat Protection
TH3 temperature exceeds 70°C or 63HS saturation temperature below 70°C.
Check system temperatures, ensure proper ventilation, and inspect sensors.
UF
Compressor Overcurrent/Lock
Overcurrent detected during compressor start-up, possible lock-up.
Inspect compressor for mechanical issues; run diagnostic tests.
UL
Open Circuit (63L)
Open circuit detected in component 63L.
Inspect the 63L circuit for disconnections or faults; repair as needed.
Incorrect refrigerant address settings or faulty communication.
Verify refrigerant address settings on SW1; check communication lines.
E1
Faulty Controller
The controller unit may be malfunctioning or damaged.
Inspect the controller for faults and replace if necessary.
E3
Transmitting Error (PAR-W21)
Incorrect refrigerant address settings.
Verify and correct refrigerant address settings on SW1.
E4
Receiving Error (PAR-W21)
Communication fault between components.
Check refrigerant address settings and verify communication lines.
E5
Receiving Error (PAR-W21)
Communication failure in refrigerant address settings.
Check address settings on SW1 and ensure secure connections.
E6
Indoor/Outdoor Communication Error
Power-up sequence issue or damaged cables.
Verify proper power-up sequence and inspect communication cables.
E8
Indoor/Outdoor Communication Error
Improper initialization or connection issues.
Inspect cables and ensure correct power-up order.
E9
Indoor/Outdoor Communication Error
Improper initialization or damaged communication lines.
Check communication cables, verify proper power-up sequence, and reset the system.
EF
Non-Defined Error Code
Possible electrical noise interference or undefined system fault.
Power down the unit for at least 30 seconds, restart, and monitor for recurring issues.
ED
Serial Communication Fault
Communication fault between the main board and inverter board, or loose CN2 or CN5 cables.
Secure connections at CN2 and CN5, and inspect communication cables for damage.
How to Troubleshoot Mitsubishi Ecodan Faults
Follow these steps to address how to fix Mitsubishi Ecodan faults:
1. Check the Display Panel: Note the fault code displayed on the controller.
2. Refer to the Manual: Use the Mitsubishi Ecodan manual or our fault code table for reference.
3. Inspect the Unit: Look for visible signs of leaks, blockages, or disconnected components.
4. Reset the System: Turn off the unit, wait a few minutes, and restart it.
5. Contact a Professional: Consult a certified technician for complex or recurring errors.
Why Is My Mitsubishi Ecodan Heat Pump Not Working?
Several common factors can cause your Mitsubishi Ecodan heat pump to malfunction:
Low Water Pressure: Ensure the system has adequate water pressure.
Sensor Faults: Thermistors or temperature sensors may fail or become disconnected.
Communication Errors: Damaged cables or loose connections can disrupt communication between the controller and the outdoor unit.
Blocked Strainer or Pipes: Debris or airlocks can reduce water circulation.
When to Call a Professional
While some Mitsubishi Ecodan error codes can be resolved with simple DIY steps, critical faults such as U6 (Inverter/Compressor Overcurrent) or E6 (Indoor/Outdoor Communication Error) should be addressed by an experienced heating engineer. Check your warranty, as the manufacturer should be your first port of call.
If you're unsure about the cause of a fault code, it’s always safer to seek professional assistance.
Proactive Maintenance Tips for Mitsubishi Ecodan Heat Pumps
Preventive maintenance can help reduce fault occurrences and extend the lifespan of your Mitsubishi Ecodan heat pump:
✔ Annual Inspections: Schedule yearly maintenance with a qualified technician.
✔ Keep Outdoor Units Clean: Remove debris, leaves, and obstructions from the outdoor unit.
✔ Monitor System Pressure: Regularly check water pressure levels.
✔ Observe Performance: Pay attention to unusual noises, reduced heating efficiency, or rising energy bills.
Frequently Asked Questions (FAQs)
Q: How do I reset my Mitsubishi Ecodan heat pump? A: Turn off the unit, wait five minutes, and restart it. If the issue persists, consult a technician.
Q: What does L3 mean on a Mitsubishi Ecodan heat pump? A: It indicates circulation water temperature overheat protection. Check for leaks, blockages, and water pump issues.
Q: How can I fix an E6 error on my Mitsubishi Ecodan? A: Ensure both indoor and outdoor units are powered on. Inspect cables for damage or loose connections.
Q: Can I troubleshoot Mitsubishi Ecodan faults myself? A: Simple faults, like checking for leaks or resetting the unit, can often be fixed at home. For complex issues, professional help is recommended.
Q: How can I prevent Mitsubishi Ecodan fault codes? A: Schedule regular maintenance, monitor pressure levels, and ensure the outdoor unit remains clean.
Conclusion
Understanding the Mitsubishi Ecodan error codes, and the fault codes, can save you time and reduce costly repairs. Identifying the issue will help you determine whether it is something you can fix yourself, or if you need professional help. If the unit is quite old, outside of the warranty and it starting to have faults more regularly then try our online quote tool to find a suitable replacement. Replacing an existing heat pump is much easier and cheaper than the initial install. Arrange a call with our team to discuss the process of replacing a heat pump.
For ongoing reliability, regular maintenance and professional inspections are essential.
Bookmark this guide for easy troubleshooting or share it with other Mitsubishi Ecodan owners!
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