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L5

Mitsubishi Electric L5 on an Ecodan heat pump: water temperature sensor fault

Verified with sources1 sourceReviewed Oct 3, 2026
Technician coming? See the 2 steps they must show you
Air-to-water heat pump outdoor unit next to a house
Mueller felixCC BY-SA 4.0Image source

Risk level

Medium

Proceed carefully and stop if the check is unclear.

Urgency

Medium

Quick answer

On Ecodan systems, L5 means a water temperature sensor reads open circuit or short circuit. Note the code and time and call the installer: measuring the sensor requires opening the cylinder.

Safety first

Stop and check this first

  • Mitsubishi Electric states that the cylinder and outdoor unit must not be disassembled, altered or repaired by the user, and that all electrical work must be done by a qualified technician. Do not open the cylinder or work on the water circuit inside it.

Safe checks you can perform

  • Code and operating mode
  • Restart from the consumer unit
  • Measuring the affected sensor

Leave these tasks to a qualified professional

  • Do not attempt this professional task: Identify and measure the sensor
  • Do not attempt this professional task: Check DIP settings before replacing the board

What a technician must be able to justify

Technician visit

These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.

These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.

  1. Identify and measure the sensor

    What they doThe technician checks which sensor is failing, measures its resistance and compares it with a hand-held thermometer.

    They must show youwhich sensor it was and its measured resistance against 4.3 to 9.5 kΩ between 10 and 30 °C.

    In writingthe sensor, the measured value and whether the sensor, the connector or nothing was replaced.

  2. Check DIP settings before replacing the board

    What they doIf the sensor measures correctly, the technician checks the DIP switches and the connector before proposing the FTC board.

    They must show youthe DIP switch positions against your system configuration.

    In writingthe setting checked, the part replaced and the test without L5.

Before accepting a part or repair

Nothing has been shown yet. Do not accept a part swap based on the code alone.

Follow these steps

Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.

  1. Code and operating mode

    No special tools

    Who:
    you.
    How:
    note the code, the time and whether the unit was heating, making hot water or cooling.
    Result that matters:
    L5 is a water sensor reading fault, not a flow or pressure fault.
    If it appears right after work on the cylinder:
    a disturbed connector is likely; tell the installer.
    If it appears with no previous work:
    no cause is ruled out; the technician identifies the sensor.
    Evidence to keep:
    a photo of the controller with the code.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

  2. Restart from the consumer unit

    No special tools

    Who:
    you.
    How:
    switch the heat pump off at its breaker, wait a few minutes and switch it back on once.
    Result that matters:
    whether L5 returns on start-up.
    If it does not return:
    it may have been a one-off reading; note the date in case it repeats.
    If it returns:
    the fault is persistent; stop resetting and call the installer.
    Evidence to keep:
    a note of the restart result.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

  3. Measuring the affected sensor

    Tools required

    Who:
    the installer or a Mitsubishi technician.
    How:
    they identify the sensor in the running information, disconnect it and measure its resistance with a multimeter, and compare the controller reading with a hand-held thermometer.
    Result that matters:
    Mitsubishi gives 4.3 to 9.5 kΩ as normal between 10 and 30 °C, and 6.3 kΩ at 20 °C.
    If it reads open, short or off the table:
    the sensor is confirmed.
    If it reads correctly and the connector is firm:
    the FTC board or the DIP setting is the suspect.
    Evidence to keep:
    a job sheet with the sensor identified, the kΩ and the reference temperature.

    Requires opening the cylinder and isolating the supply. Qualified technician only.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

Still not solved

If the error persists, stop here. See what the technician must do and show you.

Where this code applies

A code is meaningful only inside the right product and version context.

Primary scope

System
Heat pumps
Brand
Mitsubishi Electric
Product type
Air-to-water heat pump

Known code variants

  • aire acondicionado Daikin L5
  • climatisation Daikin L5
  • climatizzatore Daikin L5
  • code erreur L5 Daikin
  • codice L5 Daikin
  • código L5 Daikin
  • Daikin AC L5
  • Daikin error L5
  • Daikin Fehler L5
  • Daikin Fehlercode L5
  • Daikin L5
  • Ecodan L5
  • error L5 Daikin
  • errore L5 Daikin
  • Ideal boiler L5
  • Ideal boiler L5 too many resets
  • Ideal L05
  • Ideal L5
  • Ideal Logic L5
  • Klimaanlage Daikin L5
  • Mitsubishi Ecodan L5
  • Mitsubishi L5 heat pump
  • panne L5 Daikin

What it means

On Ecodan FTC5 cylinders, L5 covers the water sensors: flow THW1, return THW2, tank THW5 and zone sensors THW6 to THW9. The controller flags open circuit at −39 °C or below and short circuit at 88.5 °C or above. Mitsubishi lists a loose connector or wire, a faulty sensor, the FTC board or an incorrect DIP switch setting. The code does not say which sensor; the technician sees it in the running information.

Warnings and stop conditions

  • Highsource verified

    Mitsubishi Electric states that the cylinder and outdoor unit must not be disassembled, altered or repaired by the user, and that all electrical work must be done by a qualified technician. Do not open the cylinder or work on the water circuit inside it.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

Symptoms and causes

Probable causes · in order

  • Loose connector or wireCommon

    A loose connector reads as open circuit even with a good sensor. Mitsubishi asks to check it visually and reattach it.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

  • Faulty sensorPossible

    The sensor is connected but its resistance does not match the temperature. Measuring it against the maker's table confirms it.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

  • FTC board or DIP settingLess common

    If sensor and wiring measure correctly, the FTC board and a wrong DIP switch setting remain, for example after a configuration change.

    Evidence: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

Virtual technician

Does L5 still appear after these checks?

Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.

Start diagnosis

Sources and technical references

  1. 1

    Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition C

    Mitsubishi Electric · 2016 · manual

Sources: Mitsubishi Electric Ecodan FTC5 cylinder unit service manual OCH570 revised edition Creviewed 2026-10-03 · verified

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