Toshiba heat pump error codes

18 codes that Toshiba publishes for its heat pumps, each with what it means, the likely cause, what you can safely check and when to call an installer. Tap your code:

Heat pump: do only the checks the maker gives the owner for that code — read the water pressure on the controller, keep the outdoor unit clear of leaves and snow, switch the power off and on where the maker says to. Keep the casing on: refrigerant, wiring and the water circuit’s parts are not owner work. Anything else is for the heat-pump installer or the maker’s service engineer: in the UK and EU only an F-gas certified technician may open the refrigerant circuit. Codes that need one are marked Installer.

Read this first

Toshiba Estia air-to-water heat pumps show a failure code on the remote controller, such as A01 or E04, with the unit number beside it. Toshiba’s owner’s manual for the R32 Estia wall-mounted hydro units (HWT-601, HWT-1101 and HWT-1401XWH) gives the owner one step for it: contact the installation company. The meanings here come from the installation manual of the same hydro units, written for the installer, so it gives no owner checks; it does say, for each code, whether the backup heater may keep heating or hot water going and whether the unit resets itself once the cause has gone. Models differ: your model’s manual is the authority.

`A01` Pump or water flow failure

What it means: The hydro unit detected an abnormal water flow rate: almost no water, or too little, is moving. Backup operation is possible for hot water but not for heating, and the code does not reset itself.
Likely cause: Toshiba lists air not vented from the system, dirt clogging the water pipes, pipework that is too long, and a buffer tank with a secondary pump. Its symptom table adds low water pressure, a clogged strainer and a faulty 3-way valve.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: venting, the strainer and the system pressure are their work in this manual.

Source: Toshiba, Installation Manual, Air to Water Heat Pump, Hydro Unit wall mounted type HWT-601/1101/1401XWHM3W/M6W/T6W/T9W-E, R32 (2F30151001-05, 2023-02-17): Troubleshooting, failure mode detected by the Hydro Unit Checked 2026-10-13.

`A02` Water not heating up (heating)

What it means: The water temperature did not rise as expected in heating, judged by the water inlet, water outlet and heater outlet sensors (TWI, TWO, THO). Backup operation is possible for hot water, not heating; the code resets itself once the cause is gone.
Likely cause: A fault in one of those sensors, or a failed backup heater (its automatic-reset thermostat).
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`A03` Water not heating up (hot water)

What it means: The hot-water cylinder did not heat up as expected, judged by its sensor (TTW). Backup operation is possible for heating, not hot water; the code resets itself once the cause is gone.
Likely cause: The cylinder sensor, or the cylinder’s thermal cut-out.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`A04` `A10` Antifreeze operation

What it means: The unit’s frost protection acted on the water side (A04; A10 is the second antifreeze protection). Backup operation is possible; neither resets itself.
Likely cause: Almost no or little water flow — dirt in the pipes, pipework too long or too short — or, for A04, a problem in the heater’s power circuit (voltage, breaker, connection), the backup heater not set as present, or a sensor (TWI, TWO, TC) or the flow sensor.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`A05` Piping antifreeze operation

What it means: The frost protection for the pipework acted. Backup operation is possible and the code resets itself.
Likely cause: The heater’s power circuit (voltage, breaker, connection), the water inlet, outlet or heater outlet sensors, or a disconnected backup heater.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`A08` Low pressure sensor operation

What it means: The refrigerant low-pressure sensor acted. Backup operation is possible; the code does not reset itself.
Likely cause: Toshiba lists little or no water flow, a faulty flow sensor, running in cooling or a long defrost with a lot of frost, a faulty low-pressure sensor, and a refrigerant gas leak.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: refrigerant work needs an F-gas certified technician.

`A09` Backup heater overheat protection

What it means: The thermostat of the backup heater cut it out for overheating. Backup operation is possible for hot water, not heating; no automatic reset.
Likely cause: No water in the unit, or no water flow (heating without water), a faulty flow sensor, or a faulty automatic-reset thermostat on the backup heater.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`A11` Release protection

What it means: The release protection operated. Backup operation is possible for hot water, not heating; no automatic reset.
Likely cause: Almost no water flow, a faulty flow sensor, or the water outlet temperature sensor (TWO).
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`A13` `A14` `A15` Circulation pump failure

What it means: The water pump has stopped: A13 and A14 the main pump, A15 the zone 2 pump. Backup operation is possible for hot water only (A13, A14); none resets itself.
Likely cause: Low supply voltage; for A13 also high humidity or condensation around the pump’s electrics; for A14 and A15 a pump locked by dirt.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer. Toshiba tells the installer, for A13, to switch the system’s power off and on and run it again, and, for a dirt-locked pump, to free the shaft with a screwdriver.

`E03` Remote controller not communicating

What it means: Regular communication between the hydro unit and the remote controller failed. No backup operation; the code resets itself when communication returns.
Likely cause: The remote controller’s connection, or a faulty remote controller.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`E04` Indoor and outdoor unit not communicating

What it means: Regular communication between the hydro unit and the outdoor unit failed. Backup operation is possible and the code resets itself when communication returns.
Likely cause: The serial circuit between the two units, for example the connecting wires crossed during installation.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`H01` `H02` Compressor breakdown or lock

What it means: H01 compressor breakdown; H02 compressor lock. Backup operation is possible; neither resets itself.
Likely cause: For H01: the power supply voltage, an overloaded refrigeration cycle, or a service valve not fully open. For H02: a locked compressor or open-phase compressor wiring.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: the compressor is inside the sealed refrigerant circuit.

`P04` High pressure switch

What it means: The refrigerant high-pressure switch acted. Backup operation is possible; no automatic reset.
Likely cause: Little or no water flow, a faulty flow sensor, running on load in those conditions, a faulty high-pressure switch, or a refrigerant valve not opening.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer.

`P15` Gas leak detected

What it means: The outdoor unit detected a refrigerant gas leak. Backup operation is possible; no automatic reset.
Likely cause: A leak in the refrigeration cycle, a service valve not fully open, or a faulty pulse motor valve.
What you can safely check: Nothing for the owner to check: this one is for an installer.
When to call an installer: Installer Call your installer: only an F-gas certified technician may work on the refrigerant.

A code that is not listed here

The installation manual lists more check codes than these — F-codes for individual temperature sensors, L-codes for set-up errors and further P-codes from the outdoor unit. Toshiba’s instruction to the installer for all of them: do not keep the heat pump on backup operation while a check code is displayed; remove the cause straight away. For a code not listed here, note it with the unit number and call your installer.

We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.

Source

Every code on this page comes from these pages, published by Toshiba and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.

Toshiba: Installation Manual, Air to Water Heat Pump, Hydro Unit wall mounted type HWT-601/1101/1401XWHM3W/M6W/T6W/T9W-E, R32 (2F30151001-05, 2023-02-17): Troubleshooting, failure mode detected by the Hydro Unit Checked 2026-10-13.
Toshiba: Owner’s Manual, Air to Water Heat Pump, Hydro Unit wall mounted type HWT-601/1101/1401XWH (2F30152001-04, 2023-02-08): 6 Troubleshooting Checked 2026-10-13.

Toshiba heat pump error codes

Read this first

A01 Pump or water flow failure

A02 Water not heating up (heating)

A03 Water not heating up (hot water)

A04 A10 Antifreeze operation

A05 Piping antifreeze operation

A08 Low pressure sensor operation

A09 Backup heater overheat protection

A11 Release protection

A13 A14 A15 Circulation pump failure

E03 Remote controller not communicating

E04 Indoor and outdoor unit not communicating

H01 H02 Compressor breakdown or lock

P04 High pressure switch

P15 Gas leak detected