Itho Daalderop heat pump fault: A, E, F, P and S codes explained

Short answer: an Itho Daalderop heat pump (WPU, HP-S, HP Cube or Base Cube) reports faults with a letter and a number. The A codes come from the indoor controller and concern sensors, water pressure, flow and communication with the thermostat; you can often solve these yourself. The E, F and P codes come from the outdoor unit and the refrigerant circuit and are for a certified refrigerant (F-gas) technician. The S codes concern flow rate and frost protection. The two most searched codes, A1 19 and A1 20, simply mean that the central heating water pressure is too low. Below are all the groups, what you can check yourself and which part goes with each.

Which Itho Daalderop heat pump do you have?

• WPU (WPU 3, 5, WPU C/CO): ground source heat pump with a borehole, common in new builds between 2000 and 2015.
• HP-S 55, 95, 110: air-to-water heat pump with an outdoor unit and an indoor unit.
• HP Cube: hot water heat pump (cylinder) running on ventilation air.
• Base Cube: hybrid, a boiler with a heat pump section.

The rating plate is on the indoor unit or under the front panel. The complete list of all 114 codes for these appliances is in our Itho Daalderop fault codes.

The code groups in one table

Group	Comes from	What it is about	Yourself or engineer
A0	Controller	Communication with the heat pump interrupted	Yourself: plugs, reset; then an engineer
A1	Controller / indoor unit	Temperatuursensoren, druksensor, flowsensor, pressostaat, waterdruk, startstroom compressor	Water pressure yourself; sensors and pressure switch an engineer
A3	Controller	Wireless thermostats, sub-controllers, batteries, valve actuators, manual mode	Almost always yourself
E	Outdoor unit	Compressor power supply and control, PCBs, EEPROM	Engineer
F	Outdoor unit	Outdoor unit temperature and pressure sensors, fan, evaporating and condensing pressure, mixing valves	Engineer
P	Outdoor unit	Safety devices: refrigerant, input current, compressor drive, high/low pressure	Engineer, F-gas certified
S	Indoor unit	Flow rate, flow switch, frost protection, flow temperature, defrosting	Valves and filters yourself; then an engineer

The codes you can solve yourself

Code	Message	What you do
A1 19 en A1 20	Central heating system water pressure too low	Top up to 1.5 to 2 bar when cold, then bleed. If the pressure drops more often: expansion vessel or leak
A3 8 en A3 9	Batteries of a room thermostat or the main thermostat flat	Replace the batteries, reconnect the thermostat
A3 1 en A3 2	No wireless communication with a thermostat	Check distance and obstacles, batteries, re-pair the thermostat
A0 3	Communication with the heat pump interrupted	Check the power supply to the outdoor unit (fuse), bus cable and plugs; then reset
A3 13	Controller is in manual mode	Switch back to automatic in the menu
S02 en S10	Flow rate too low	Open radiator and underfloor heating valves, clean the filter or dirt separator, bleed; if it persists: pump or flow switch
P09	Outdoor unit air circulation inadequate	Remove leaves, snow and obstacles around the outdoor unit, at least 30 cm clearance
S08	Defrosting failed three times	Let the ice on the evaporator melt; if it comes back in normal weather: read here what is normal

The codes that come with a part

Code	Message	Part
A1 1 to A1 11	Temperature out of range or sensor open circuit/short-circuited	Temperature sensor HP-S € 18.95, sensor 22 mm WPU € 20.95, outdoor sensor WPU € 48.95
A1 12	CH pressure sensor not working	CH water-side pressure sensor € 37.95
A1 15	Borehole flow sensor faulty	Flow sensor; have the borehole circuit bled first
A1 17 en A1 18	Pressure switch (high-pressure switch) activated or faulty	Engineer: too little flow or too much refrigerant pressure
F03	Compressor discharge gas temperature sensor	Discharge gas temperature sensor HP-S € 18.95
F09 en F10	Fan not reaching its speed	DC fan motor HP-S € 130.95 or reconditioned fan HP Cube € 165.95
F29 en F30	Mixing valve 1 or 2	4-way valve HP-S € 45.95, diverter valve WPU € 122.95
E05, P03	Compressor or compressor drive fault	PCB compressor HP-S 55 € 301.95; compressor itself: when replacement pays off
Pump not running, pump making noise	Fuse, cavitation due to low pressure	Circulation pump HP-S € 384.95, CH pump Cube € 254.95
E01, F25	Communication between control panel and indoor unit	Control panel HP-S € 292.95, WPU 2 controller € 423.95

All parts for these appliances can be found under Itho Daalderop parts; prices include VAT.

What you should never do yourself

Anything involving the refrigerant circuit (P codes, F05, F06, F11, F12) and the compressor and its power supply (E codes) is work for a certified refrigerant (F-gas) technician. With a Base Cube, the boiler section is also a gas combustion appliance: burner, gas valve and flue only by a certified gas engineer. Sensors, valves and the pump on the water side can, however, be replaced by an installer without refrigeration qualifications.

Before you call an engineer

• Note the complete code and the text on the display, and whether it comes back after a reset.
• Check the water pressure on the indoor unit and top up if necessary.
• Check that the outdoor unit has power and is unobstructed, and whether the fan runs when the heat pump calls for heat.
• For thermostat codes (A3): batteries and distance.
• Photograph the rating plate; with the type and the code we can have the part ready in advance, so your installer can finish the job in one visit.

Is de warmtepomp aan vervanging toe, dan vindt u de actuele modellen bij · .

Frequently asked questions

What does A1 20 mean on my Itho Daalderop heat pump?

The water pressure in the heating system is too low. Top up to 1.5 to 2 bar when cold and bleed the system. If the message returns within a few weeks, you are losing water or the expansion vessel has failed.

Can I reset the heat pump?

Yes, once. If the same code comes back, have the cause investigated. With P codes (safety cut-outs), do not keep resetting: the compressor can be damaged.

Why does my WPU show an A3 code when the unit is working normally?

A3 codes relate to the controller and the thermostats, not the heat pump. The unit usually keeps running on the last known setting. Flat batteries are the most common cause.

Are Itho Daalderop parts still available for a WPU from 2008?

For the most part, yes: sensors, valves, the controls and the pump are available. Some circuit boards are supplied as a service kit in a newer version. Send us the details from the rating plate and we will check availability.