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Daikin Altherma fault HJ-10

Water pressure sensor abnormality

Heat pump

What it means

Water pressure input from the water pressure sensor is out of range.

Likely causes

  1. Main water supply or pressure outside expected range
  2. Leak in the water circuit
  3. Faulty water pressure sensor
  4. Faulty hydro PCB
  5. Faulty refrigerant pressure sensor
  6. Poor water flow through high pressure side plate heat exchanger
  7. Incorrect refrigerant charge
  8. Deviation of refrigerant pressure sensor (higher value measured than actual).

Where to start

  1. Check the main water supply and pressure of the installation
  2. Check for leaks in the water circuit
  3. Perform a check of the water pressure sensor

The full answer, free

  • 4 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 52), 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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