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Heat pumps · Error codes · Toshiba
A11Toshiba

A11 on a Toshiba heat pump: Operation of the release protection

Short answer

On a Toshiba heat pump, A11 means: Operation of the release protection. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 4 sources

What it means

On the R32 Estia 1-Series (split, Wall-Mounted and All-in-One)

The manual says: Operation of the release protection.

Part involved: circulation pump, flow switch/sensor, strainer, water pipework.

When it shows: TWO release protection counts to 10.

Likely causes:

  • Almost no water flow.
  • Flow sensor defect.
  • Water outlet sensor TWO.

On the Estia (Series 4) Standard & Powerful

The manual says: Operation of the release protection.

Part involved: circulation pump, flow switch/sensor, strainer, water pipework.

When it shows: TWO release counts to 10.

Likely causes:

  • Almost no water flow.
  • Flow switch defect.
  • TWO sensor.

On the Estia 5 Series (Standard)

The manual says: Operation of the release protection.

Part involved: circulation pump, flow switch/sensor, strainer, water pipework.

When it shows: TWO release counts to 10.

Likely causes:

  • Almost no water flow.
  • Flow switch defect.
  • TWO sensor.

On the Estia 5 Series Powerful (Hi Power / Extreme)

The manual says: Operation of the release protection.

Part involved: circulation pump, flow switch/sensor, strainer, water pipework.

When it shows: Trigger thresholds not printed in the IM; see SM.

Likely causes:

  • Almost no water flow.
  • Flow switch defect.
  • TWO sensor.

Is it safe?

Does the heat pump stop?Partly
SeverityFault — needs a manual reset once the cause is fixed
Engineer needed?Yes

The heat pump keeps running with some functions stopped.

Resetting itself: no.

Manual reset: Cause must be fixed by an engineer; hardware faults reappear until repaired.

What you can check

  • Note the check code shown on the remote controller and the outdoor/hydro model numbers before contacting an engineer.
  • Check the system pressure gauge on the hydro unit / heating system shows the normal fill pressure the installer set (the manuals ask for at least about 1 bar); if it is low, report it to the engineer. Check the filling loop is closed.
  • Check radiator/underfloor zone valves and thermostats are calling for heat and have not all been turned off.

What the engineer will check

On the R32 Estia 1-Series (split, Wall-Mounted and All-in-One)

  • Follow manufacturer's check-code flowchart.
  • Almost no water flow.
  • Flow sensor defect.
  • Water outlet sensor TWO.

Who to ask for: Heat pump / heating engineer (hydronic).

Certification: Heat pump installer competence (e.g. MCS-installer staff); no F-gas needed unless refrigerant work follows.

On the Estia (Series 4) Standard & Powerful

  • Follow manufacturer's check-code flowchart.
  • Almost no water flow.
  • Flow switch defect.
  • TWO sensor.

Who to ask for: Heat pump / heating engineer (hydronic).

Certification: Heat pump installer competence (e.g. MCS-installer staff); no F-gas needed unless refrigerant work follows.

On the Estia 5 Series (Standard)

  • Follow manufacturer's check-code flowchart.
  • Almost no water flow.
  • Flow switch defect.
  • TWO sensor.

Who to ask for: Heat pump / heating engineer (hydronic).

Certification: Heat pump installer competence (e.g. MCS-installer staff); no F-gas needed unless refrigerant work follows.

On the Estia 5 Series Powerful (Hi Power / Extreme)

  • Follow manufacturer's check-code flowchart.
  • Almost no water flow.
  • Flow switch defect.
  • TWO sensor.

Who to ask for: Heat pump / heating engineer (hydronic).

Certification: Heat pump installer competence (e.g. MCS-installer staff); no F-gas needed unless refrigerant work follows.

What you might notice

Sources

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026