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Mitsubishi Ecodan fault LD

Boiler temperature thermistor (THWB1, THWB2) failure

Heat pump

What it means

Failure of boiler temperature thermistors THWB1 or THWB2. Refer to error codes (P1/P2/L5/LD) for diagnosis and action.

Likely causes

  1. Connector/terminal wire has become detached or loose wiring
  2. Thermistor fault
  3. FTC board failure
  4. Incorrect setting of the DIP switch(es)
  5. Failed thermistor TH1A, TH2, THW1, THW2, THWB1, THW5, THWB2, TH1B, THW6, THW7, THW8, or THW9

Where to start

  1. Visually check the terminals and connections and reattach as appropriate
  2. Check resistance of thermistor against table in section 10-6
  3. Compare FTC detected temperature to hand held detector

The full answer, free

  • 3 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 50), right under the answer
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Safety: Isolate the outdoor unit and any backup heater, and give the inverter capacitors time to discharge before you open the electrics. Anything on the refrigerant circuit needs F-gas certification.

From the Mitsubishi manual for the Ecodan. Check the model on the data plate before you order parts.

Other Mitsubishi Ecodan fault codes