Itho Daalderop heat pump faults: fault codes, causes and parts

All 125 fault codes for Itho Daalderop heat pumps, plus the faults that show no code. Type your code or choose your symptom.

In brief

A fault on an Itho Daalderop heat pump usually means that the appliance has locked out or is reporting a fault code. Note the code on the display and look it up below: for each code you will find its meaning, checks you can safely do yourself and the parts that are often checked or replaced. Frequently searched: A1 20 (the water pressure of the heating system…), Knippert red (under-/overvoltage), A3 2 (no RF communication between a room thermostat…). No code? Check the power supply, the settings and the filters, and reset once. If the fault comes back, call in a qualified professional.

Most searched Itho Daalderop faults

These are the codes that visitors to this site search for most often.

A1 20The water pressure of the heating system…Flashing redUnder-/overvoltage. Pump module temperature too high.A3 2No RF communication between a room thermostat…A1 26The compressor current consumption is too high.A1 1Temperature is outside the normal operating range…A1 10Temperature is outside the normal operating range…A3 3No communication between the main controller and…A0 3Communication with the heat pump has been…

See the 25 most searched fault codes of 2026, with the figures behind them →

Itho Daalderop heat pump faults without a code on the display

Not every fault shows a code. These are the symptoms we come across most often with Itho Daalderop appliances, with what you can check yourself before calling someone out.

Heat pump no longer produces heat

Check that the system has enough pressure and whether there is a message on the display or in the app. After a power cut, some units start up in a safe mode and have to be released manually. View the matching parts → Read also: heat pump freezes or defrosts constantly →

Outdoor unit freezes or defrosts constantly

A thin layer of ice in frosty weather is normal; the unit defrosts itself periodically. If the ice stays or the unit defrosts every few minutes, the airflow is obstructed or something is wrong with the defrost control. View the matching parts → Read also: heat pump freezes or defrosts constantly →

Too little or too cold hot water

Check the set hot water temperature and whether the electric immersion heater is enabled. A sharp drop in hot water capacity often points to a faulty cylinder sensor or a worn anode in the tank. View the matching parts → Read also: replace the anode before the tank fails →

Noise or vibrations

A noticeably louder noise than normal usually comes from the fan or from vibrations carried through the pipework. Check that the unit stands clear and that the anti-vibration mounts are intact. View the matching parts → Read also: noise and ice on the outdoor unit →

All 125 Itho Daalderop heat pump fault codes

Code	Cause
A0 3	Communication with the heat pump has been interrupted.
A1 1	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 10	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 11	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 12	Heating pressure sensor is not functioning properly or is defective.
A1 13	Current measuring coil not functioning properly or is faulty.
A1 14	Current measuring coil not functioning properly or is faulty.
A1 15	Source flow sensor is not functioning properly or is defective.
A1 16	An automatic function or setting has been changed to manual operation.
A1 17	The pressure switch (high pressure switch) has been activated.
A1 18	The pressure switch (high pressure switch) is not functioning properly or is defective.
A1 19	The water pressure of the heating system is too low.
A1 2	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 20	The water pressure of the heating system is too low.
A1 21	The compressor starting current is too high. The compressor temperature protection is not functioning properly or is faulty.
A1 21	The compressor starting current is too high.
A1 21	The compressor temperature protection is not functioning properly or is defective.
A1 22	The phase sequence in the wall socket is not clockwise on the heat pump.
A1 23	There is no clockwise rotating field on the incoming 3-phase supply to the heat pump.
A1 24	The compressor current consumption is too low.
A1 25	The electric heating element current consumption is too low.
A1 26	The compressor current consumption is too high.
A1 27	The electric heating element current consumption is too high.
A1 28	The source return temperature (T8) is too low.
A1 29	The source flow temperature (T9) is too low.
A1 3	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 30	The liquid temperature (T7) is too high.
A1 31	The discharge gas temperature (T6) is too high.
A1 32	The injection temperature (T4) is too low.
A1 33	Discharge gas temperature too high in relation to the liquid temperature and the expansion valve is fully open.
A1 34	The heating flow temperature (T10) is too high.
A1 34	The heating flow temperature (T10) is too high.
A1 36	Thermostat communication fault.
A1 37	Compressor current consumption without control signal.
A1 38	The element relay is stuck.
A1 4	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 42	Temperature sensors T8 (source return) and T9 (source flow) are not functioning properly or are defective.
A1 43	An unsuitable thermostat is connected.
A1 5	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 6	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 7	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 8	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A1 9	Temperature is outside the normal operating range or the sensor has an open circuit or short circuit.
A3 1	No wireless communication between the main thermostat and the controller for too long.
A3 10	The temperature sensor of the main thermostat is defective.
A3 11	The temperature sensor of a room thermostat is defective.
A3 13	The controller is in manual mode.
A3 2	No RF communication between a room thermostat and the controller for too long.
A3 3	No communication between the main controller and sub-controller 1 for too long.
A3 4	No communication between the main controller and sub-controller 2 for too long.
A3 5	Configuration not completed properly.
A3 6	A valve actuator does not respond.
A3 8	The batteries of a room thermostat must be replaced.
A3 9	The batteries of the main thermostat must be replaced.
Continu green	Normal operation
Continu red	Rotor blocked.
Continu red	Winding defective.
E01	There is a fault in the communication between the control panel and the indoor unit. This is probably a PCB fault.
E02	There is a fault in the communication between the main control PCB and the module PCB of the outdoor unit.
E03	There is a fault in the current supply to the compressor.
E04	There is a fault in the current supply to the compressor.
E05	There is a fault in the compressor.
E06	There is a fault in the VDC module. The voltage is too high or too low.
E07	There is a fault in the AC voltage.
E08	There is a fault on the EEPROM.
F01	The outdoor temperature sensor of the outdoor unit has a fault.
F02	The evaporator temperature sensor of the outdoor unit has a fault.
F03	The compressor discharge gas temperature sensor has a fault.
F04	The suction gas temperature sensor of the outdoor unit has a fault.
F05	The evaporating pressure sensor has a fault.
F06	The condensing pressure sensor has a fault.
F07	The high/low pressure switch is open while the heat pump is in standby, or 2 minutes after the compressor has been stopped.
F09	The DC fan or fans (in a system with two fans) cannot reach the required speed or there is no feedback signal.
F10	The fan(s) cannot reach the required speed or there is no feedback signal.
F11	The evaporating pressure is too low.
F12	The condensing pressure is too high.
F13	There is a fault in temperature sensor Tr.
F14	There is a fault in temperature sensor Tw.
F15	There is a fault in temperature sensor Tc.
F16	There is a fault in temperature sensor Tuo.
F17	There is a fault in temperature sensor Tui.
F18	There is a fault in temperature sensor Tup.
F21	There is a fault in temperature sensor Tv1.
F22	There is a fault in temperature sensor Tv2.
F25	There is a fault in the communication between the control panel and the PCB of the indoor unit or outdoor unit.
F27	There is a fault on the EEPROM of the indoor unit.
F28	There is a fault on the PWM feedback signal.
F29	There is a fault on mixing valve 1.
F30	There is a fault on mixing valve 2.
Flashing red	Under-/overvoltage. Pump module temperature too high.
Knippert red/green	Dry running
Knippert red/green	Overload
P01	Evacuation was not carried out correctly during installation and air has entered the refrigerant system.
P01	There is too much refrigerant in the system.
P01	The air flow through the outdoor unit is insufficient.
P01	The input current is too high or too low, or the system is overloaded.
P02	The input current is too high or too low, or the system is overloaded.
P03	Compressor drive fault.
P04	If the compressor runs continuously at low speed for an extended period, this protection is activated to draw the compressor oil back into the compressor
P05	Compressor is switched off because the high/low pressure switch has opened due to abnormally high/low pressure.
P06	Compressor speed drops because abnormally high pressure is detected by the condensing pressure sensor.
P07	When the compressor has been stationary for a long time and the outdoor temperature is low, the compressor crankcase heater is switched on for some time to hot up the compressor before it starts.
P08	Flow temperature too high or flow rate too low or insufficient refrigerant.
P09	Air circulation of the outdoor unit not adequate.
P10	The input voltage of the heat pump is too high or too low.
P11	Compressor is switched off because the outdoor temperature is too high/low.
P12	Compressor is limited as a result of too high/low outdoor temperature.
P14	The compressor speed drops because abnormally low pressure is detected by the condensing pressure sensor
Pump not running	Electrical fuse defective.
Pump not running	Pump has no supply voltage.
Pomp maakt geluiden	Cavitation due to low system pressure
S01	There is a fault in the anti-freeze protection of the indoor unit cooling. The compressor speed is reduced if the exchanger temperature is lower than 2 ℃; the compressor is stopped if the exchanger temperature is lower than -1 ℃; the compressor is restarted if the exchanger temperature is higher than 6 ℃.
S02	The flow rate in the system is lower than permitted. (HP-S 55 minimum 600 l/h, HP-S 95 and HP-S 130 minimum 900 l/h)
S03	The flow switch is not working.
S04	Too much data is lost during communication.
S05	A fault has occurred in the communication between the control panel and the PCB of the indoor unit or the outdoor unit.
S06	The flow temperature during cooling is lower than 5°C. The compressor is stopped if the flow temperature in cooling mode is lower than 5 ℃.
S07	The flow temperature during heating / domestic hot water production is higher than permitted. The compressor is stopped if the flow temperature in heating or hot water mode is higher than 57 ℃.
S08	Defrost process unsuccessful after being initiated three times. Normal operation of the system can only be restored by restarting it.
S09	The flow temperature during heating / DHW production is too low.
S10	The water flow rate is too low.
S11	Frost protection during cooling has been activated.
Uit	Energy saving during standby of the heat pump.
Uit	No power supply.
Uit	LED lighting defective.

Order parts for your Itho Daalderop heat pump

Itho Daalderop parts are available from Instalpunt; shipping to EU countries from €12.95 (€16.95 for more distant countries), usually 3–5 working days.

View Itho Daalderop parts →

Frequently asked questions about Itho Daalderop faults

What does a fault on an Itho Daalderop heat pump mean?

The appliance is reporting that it has shut itself down or cannot continue. The code on the display points to the group of causes: ignition, water pressure, a sensor, the fan or communication with the thermostat. The table above shows, for each code, what Itho Daalderop means by it.

How do I reset my Itho Daalderop heat pump?

The reset button is on the control panel of your Itho Daalderop heat pump; on most appliances you hold it down for two to five seconds until the display responds. Reset once. If the same fault comes straight back, resetting will not solve it and a part or a setting needs attention. Always consult the manual for your model: the position of the button and how long to press it differ per series.

Can I fix an Itho Daalderop fault myself?

You can top up the water pressure, bleed the system, replace filters and clean a siphon yourself. Anything behind the sealed section of a gas appliance is a different matter: work on the gas valve, burner, heat exchanger and flue must be carried out by a certified gas engineer.

How much does it cost to fix a fault?

That depends on the cause and whether a part is needed. With us you can see the part straight away with its price and delivery time, so you know where you stand in advance. If you call in an engineer, always ask about the call-out charge and hourly rate before they come.

Where can I find the right part for my Itho Daalderop?

Check the rating plate for the exact type and use it to search our catalogue, or search directly by the manufacturer number of the faulty part. Each part lists the appliances it fits.