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Daikin Altherma fault U0-00

Outdoor unit: shortage of refrigerant

Heat pump

What it means

Refrigerant shortage detected in the outdoor unit refrigerant circuit; unit will stop operating.

Likely causes

  1. Faulty refrigerant side thermistor(s)
  2. Faulty refrigerant pressure sensor
  3. Closed stop valve in the refrigerant circuit
  4. Clogged refrigerant circuit
  5. Refrigerant shortage
  6. Non-condensables and/or humidity in the refrigerant circuit
  7. Faulty compressor or miswiring of the compressor power supply cable
  8. Faulty expansion valve
  9. Leak in the refrigerant circuit

Where to start

  1. Perform a check of all refrigerant side thermistors
  2. Perform a check of the refrigerant pressure sensor
  3. Check that all stop valves of the refrigerant circuit are open

The full answer, free

  • 7 more checks in order
  • How to put it right, step by step
  • The manual page for this fault (page 58), 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 Daikin manual for the Altherma. Check the model on the data plate before you order parts.

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