L5 • Mitsubishi Electric • Ecodan (Air/Eau)
Fault code L5 Mitsubishi Ecodan: Water flow fault
Specific to Ecodan air-to-water heat pumps, L5 indicates a water circulation anomaly. The heat exchanger temperature rises too quickly or the flow meter detects nothing.
Proof status : Manufacturer reference needed for the exact range
Source: Mitsubishi Electric Ecodan FTC Service Manual
Founder, AskMarcel.app
Founder of AskMarcel.app. Sheets are written from manufacturer documentation; the reference is shown when it has been verified.
In brief
Fault code L5 on Mitsubishi Electric Ecodan (Air/Eau) means: Specific to Ecodan air-to-water heat pumps, L5 indicates a water circulation anomaly. The heat exchanger temperature rises too quickly or the flow meter detects nothing. Most common cause: Dirty strainer filter, closed valves, air in the circuit, or seized/faulty circulator pump. First action: Close the isolation valves and clean the magnetic strainer filter.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).
According to the Mitsubishi Electric Ecodan FTC Service Manual, the L5 fault code specifically indicates a failure of the indoor unit temperature thermistor, affecting sensors THW1 through THW9.
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Mitsubishi Electric code L5: Marcel picks this code up for Ecodan (Air/Eau) and guides you, with the manufacturer reference when one exists.
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What does fault code L5 on Mitsubishi Electric mean?
Specific to Ecodan air-to-water heat pumps, L5 indicates a water circulation anomaly. The heat exchanger temperature rises too quickly or the flow meter detects nothing.
Dirty strainer filter, closed valves, air in the circuit, or seized/faulty circulator pump.
Symptoms
- No heating or hot water
- Hydraulic module is silent
- Code L5 on FTC interface
Diagnosis
1. Filter cleaning
- Close the isolation valves and clean the magnetic strainer filter.
- This is the cause in 80% of cases.
2. Bleeding and circulator pump
- Check that the circulator pump is running (central screw or vibration).
- Bleed air from the circuit.
Repair and return to service — Mitsubishi Electric fault L5
Restore nominal water flow. If the filter is clean and the pump runs, check the water temperature sensors.
When should you call an F-Gas engineer?
Contact an F-Gas registered engineer if the fault returns after basic checks, involves refrigerant charging, or requires PCB or compressor replacement on Mitsubishi Electric Ecodan (Air/Eau).
Affected models
- Ecodan ATW (PUZ WZ)
- Ecodan Air/Eau (general)
Field context
This code appears when the diagnostic system detects a temperature reading anomaly at the indoor unit. Unlike water circulation problems (strainer, closed valves), L5 indicates a hardware fault of the temperature sensor itself, preventing the unit from
Frequently asked questions
Which components are affected by fault code L5?
Code L5 specifically affects the indoor unit temperature thermistors identified by references THW1, THW2, THW5A, THW5B, THW6, THW7, THW8 and THW9. A failure of any of these sensors triggers the error.
What is the diagnostic procedure for code L5?
To diagnose this code, measure the electrical resistance across each affected thermistor (THW1 to THW9). If the measured value is outside the manufacturer's technical specifications, the thermistor must be replaced.
Is code L5 related to a water flow problem?
No, although the initial summary may mention water circulation, the manual extracts specify that code L5 exclusively indicates a failure of the indoor unit temperature thermistor. Water flow or strainer issues fall under other diagnostics.
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