Heat pump fault codes

Vaillant heat pump faults: fault codes, causes and parts

All 227 fault codes for Vaillant heat pumps, plus the faults that show no code. Type your code or choose your symptom.

In brief

A fault on a Vaillant 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: F.9998 (cable not connected or incorrectly connected), F.723 (pressure loss in the emitter circuit due…), F.733 (no flow in the ambient circuit (heating…). 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 Vaillant faults

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

F.9998Cable not connected or incorrectly connected. Outdoor…F.723Pressure loss in the emitter circuit due…F.733No flow in the ambient circuit (heating…F.732The compressor outlet temperature is above 130°C:…F.1100The safety temperature limiter of the electric…F.532Isolating valve was not opened, emitter circuit…F.103Wrong thermostat PCB installed on the outdoor…F.788The electronics of the high-efficiency pump have…

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

Vaillant 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 Vaillant 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 →

Vaillant heat pump fault codes 1 to 150 of 227

The code list is split over 2 pages. Looking for a specific code? Use the search at the top of this page: it searches all 227 codes in one go.

Code	Cause
F.002	Too little water in the heating system
F.022	Pressure loss in the emitter circuit due to leak or air pocket, emitter circuit pressure sensor defective
F.022	Water pressure sensor defective, open circuit in the wiring harness, solenoid valve of the automatic filling device defective, internal expansion vessel defective
F.037	Obstruction in the air duct of the product, fan motor defective or not connected, connection between the main PCB and the fan PCB damaged or open circuit
F.042	The product coding resistor is defective or missing, fan motor defective or not connected, plug X25 not connected or incorrectly connected
F.042	Coding resistor damaged or not fitted
F.042	Open circuit in the heat exchanger wiring harness
F.042	Sensor not connected or sensor input short-circuited
F.070	Replacement of the control PCB and display PCB
F.070	Replace the control PCB and display PCB
F.073	Sensor not connected or sensor input short-circuited
F.073	Wire to the water pressure sensor is open circuit or has a short circuit
F.086	Contact S20 on the heat pump main PCB (HMU) open, incorrect setting of the maximum thermostat, flow temperature sensor (heat pump, gas boiler, system sensor) measures values that deviate downwards
F.086	Floor temperature is too high, flow rate of the heating circuit too low, underfloor heating circuit is closed
F.094	Flow rate sensor not connected or sensor input short-circuited
F.103	Wrong thermostat PCB installed on the outdoor unit
F.103	Parameter ""Max. duration of the circuit breaker"" is set incorrectly (see ""Heat pump setting parameters"" in the appendix), the main PCB or inverter installed as a spare part does not match the product
F.1100	The safety temperature limiter of the electric auxiliary heater has opened due to: flow rate too low or air in the emitter circuit, heating element in operation with emitter circuit not filled, heating element in operation at flow temperatures above 95°C causes the thermal fuse of the safety temperature limiter to blow and requires replacement, supply of external heat into the ambient circuit
F.1100	The safety temperature limiter of the electric auxiliary heater has opened due to: flow rate too low or air in the emitter circuit, heating element in operation with emitter circuit not filled, heating element in operation at flow temperatures above 110°C causes the thermal fuse of the safety temperature limiter to blow and requires replacement, supply of external heat into the ambient circuit
F.1100	The safety temperature limiter of the electric auxiliary heater has opened due to: flow rate too low or air in the emitter circuit and/or heating element in operation with emitter circuit not filled and/or thermal fuse of the safety temperature limiter blown and requires replacement and/or supply of external heat into the ambient circuit.
F.1100	The safety temperature limiter of the electric auxiliary heater has opened due to: flow rate too low or air in the emitter circuit, heating element in operation with emitter circuit not filled, heating element in operation at flow temperatures above 98°C causes the thermal fuse of the safety temperature limiter to blow and requires replacement, supply of external heat into the ambient circuit
F.1100	The safety temperature limiter of the electric backup heater has opened due to: – insufficient flow rate or air in the heat emission circuit, – operation of the electric heating element with the heat emission circuit not filled, – operation of the electric heating element at flow temperatures above 95 °C activates the thermal fuse of the safety temperature limiter and requires replacement, – supply of external heat into the heat emission circuit.
F.1117	Fuse defective, incorrect electrical connections, mains voltage too low, power supply to compressor/low tariff not connected, utility blocking time more than three hours
F.1117	Soft starter defective or incorrectly connected
F.1117	Soft starter defective or incorrectly connected, fuse defective, poorly tightened electrical connections, mains voltage too low, power supply to compressor/low tariff not connected, utility blocking time more than three hours
F.1118	Incorrect phase sequence of the connection to the mains supply, soft starter defective or incorrectly connected
F.1118	Incorrect phase sequence of the connection to the mains supply, soft starter defective or incorrectly connected
F.1119	Soft starter defective or incorrectly connected, mains voltage too low
F.1119	Soft starter defective or incorrectly connected, mains voltage too low
F.1120	Line protection switch in the switch cabinet has tripped, electric auxiliary heater defective, poorly tightened electrical connections, mains voltage too low, utility blocking time more than three hours
F.1120	Electric auxiliary heater defective, poorly tightened electrical connections, mains voltage too low, utility blocking time more than three hours
F.1120	Electric auxiliary heater defective, poorly tightened electrical connections, mains voltage too low
F.1120	Electric auxiliary heater defective. Poorly tightened electrical connections. Mains voltage too low.
F.1288	Sensor defective or not correctly connected to the VWZ AI heat pump control module.
F.279	The hot gas thermostat switches off the heat pump if the pressure in the refrigerant circuit is too high. After a waiting time, a further start attempt of the heat pump follows. After three consecutive failed start attempts, an error message is displayed. Refrigerant circuit temperature max.: 130 °C. Waiting time: 5 min (after the first occurrence). Waiting time: 30 min. (after the second and each subsequent occurrence). Fault counter is reset when both conditions occur: heat demand without premature switch-off. 60 min undisturbed operation.
F.283	Electric auxiliary heater insufficient or not available. Insufficient heat energy in the domestic installation. Ice formation on evaporator.
F.504	Wiring harness not correctly connected to the PCB, open circuit in the wiring harness, short circuit in the wiring harness, fan blocked, fan defective
F.514	Temperature sensor at compressor inlet defective or not connected
F.514	Sensor not connected or sensor input short-circuited
F.514	Sensor not connected or sensor input short-circuited
F.514	Sensor not connected or sensor input short-circuited
F.514	Sensor defective or not correctly connected to the main PCB
F.517	Sensor not connected or sensor input short-circuited
F.517	Sensor not connected or sensor input short-circuited
F.517	Sensor not connected or sensor input short-circuited
F.517	Sensor defective or not correctly connected to the main PCB
F.517	Temperature sensor at compressor outlet defective or not connected
F.519	Return temperature sensor on the heat pump defective or not connected
F.519	Sensor not connected or sensor input short-circuited
F.519	Sensor not connected or sensor input short-circuited
F.519	Sensor not connected or sensor input short-circuited
F.519	Sensor defective or not correctly connected to the main PCB
F.520	Sensor not connected or sensor input short-circuited
F.520	Sensor not connected or sensor input short-circuited
F.520	Sensor not connected or sensor input short-circuited
F.520	Sensor defective or not correctly connected to the main PCB
F.520	Flow temperature sensor on the heat pump defective or not connected
F.523	Wire to temperature sensor VF1 is open circuit or has a short circuit
F.526	Sensor defective or not correctly connected to the main PCB
F.526	Sensor not connected or sensor input short-circuited
F.526	Temperature sensor not connected or sensor input short-circuited.
F.532	Isolating valve was not opened, emitter circuit pump defective, all consumers in the heating system are closed, flow too low for detection by the flow rate sensor (< 120 l/h)"
F.532	Isolating valve was not opened. Emitter circuit pump defective. All consumers in the heating system are closed. Flow rate too low for detection by the flow rate sensor (< 120 l/h)"
F.532	Isolating valve was not opened, emitter circuit pump defective, all consumers in the heating system are closed, flow rate too low for detection by the flow rate sensor (< 120 l/h), thermostatic valve(s) defective, no bypass present in systems without buffer, bypass incorrectly set or defective, air in the heat pump, minimum capacity of the pump or pump defective, condenser fouled, existing dirt filter blocked
F.532	Heating circuit not completely vented, dirt filter in return missing or blocked, lack of water - pressure loss in the heating circuit, pump defective: Check the specific flow rate in the heating circuit in the sensor/actuator test
F.536	Amount of refrigerant too low, sensor defective or not correctly connected to the main PCB, premature expansion in the liquid range of the refrigerant circuit (charge loss), electronic expansion valve defective, heat exchanger blocked
F.537	Amount of refrigerant too high or too low, vacuum not sufficient (10 mbar), refrigerant contamination, pressure switch or electrical connection defective, premature expansion in the liquid range of the refrigerant circuit (charge loss), flow rate too high (see specified maximum flow rate), flow monitor defective, heat transfer in the heat exchanger not sufficient
F.539	Amount of refrigerant too low, air flow too low, no defrosting, resistance heater in the condensate tray defective, four-way valve defective, motor of the electronic expansion valve defective or connection defective
F.546	Wiring defective
F.546	Sensor not connected or sensor input short-circuited
F.546	Sensor not connected or sensor input short-circuited
F.546	Sensor not connected or sensor input short-circuited
F.546	Refrigerant circuit pressure sensor defective or not connected
F.554	Amount of refrigerant too high or too low, refrigerant contamination (F-gas), electronic expansion valve defective, premature expansion in the liquid range of the refrigerant circuit (charge loss), flow rate too high (see specified maximum flow rate), insufficient heat exchange at the plate heat exchanger or at the finned-tube heat exchanger, four-way valve defective, temperature sensor defective
F.582	Cable insulation defective, connection interrupted
F.582	EEV not correctly connected or broken cable to the coil
F.583	Four-way valve is mechanically blocked, temperature sensor in the flow is defective, air in the emitter circuit
F.583	Four-way valve is mechanically blocked. Temperature sensor in the flow is defective. Air in the emitter circuit
F.583	Four-way valve is mechanically blocked, temperature sensor in the flow is defective, air in the emitter circuit
F.585	Sensor not connected or sensor input short-circuited
F.585	Sensor defective or not correctly connected to the main PCB
F.585	Sensor not connected or sensor input short-circuited
F.685	Thermostat VRC 470 was already detected, but the connection has been lost
F.685	System thermostat was already detected, but the connection has been lost
F.685	The product is not connected to the thermostat, polarity reversed
F.685	System thermostat was already detected, but the connection has been lost
F.700	Sensor not connected or sensor input short-circuited
F.701	Sensor not connected or sensor input short-circuited
F.701	Sensor not connected or sensor input short-circuited
F.702	Sensor not connected or sensor input short-circuited
F.702	Sensor not connected or sensor input short-circuited
F.703	Sensor not connected or sensor input short-circuited
F.703	Sensor not connected or sensor input short-circuited
F.703	Sensor not connected or sensor input short-circuited
F.704	Sensor not connected or sensor input short-circuited
F.704	Sensor not connected or sensor input short-circuited
F.705	Sensor not connected or sensor input short-circuited
F.705	Sensor not connected or sensor input short-circuited
F.706	Sensor not connected or sensor input short-circuited
F.708	No electrical connection No eBUS connection
F.708	No electrical connection, no eBUS connection
F.710	Ambient circuit pump defective, temperature sensor fault at ambient circuit outlet defective, flow rate in the ambient circuit too low, air in ambient circuit
F.710	Ambient circuit pump defective, temperature sensor at ambient circuit outlet defective, flow rate in the ambient circuit too low, air in ambient circuit, device identification setting (DSN) was not transferred when the thermostat PCB (HMU) was replaced, frost protection setting was not transferred when the thermostat PCB (HMU) was replaced
F.710	Ambient circuit pump defective, temperature sensor fault at ambient circuit outlet defective, flow rate in the ambient circuit too low
F.714	Pressure drop in the environmental circuit due to leak or air, ambient circuit pressure sensor defective
F.714	Pressure loss in the ambient circuit due to leak or air pocket, ambient circuit pressure sensor defective
F.715	The electronics of the high-efficiency pump has detected a fault (e.g. dry running, blockage, overvoltage, undervoltage) and has locked out.
F.715	The electronics of the high-efficiency pump have detected a fault (e.g. dry running, blockage, overvoltage, undervoltage) and have switched off with lockout, air in ambient circuit, viscosity of the brine is too high
F.715	Fault in the electronics of the high-efficiency pump (e.g. dry running, blockage, overvoltage, undervoltage) and switched off with lockout.
F.718	Confirmation signal missing, the fan is rotating.
F.718	Confirmation signal that the fan is rotating is missing
F.719	Defroster safety temperature limiter open, defroster fault
F.719	The safety temperature limiter of the defroster has opened due to flow rate too low or brine temperatures above 65 °C, use of the defroster outside the permitted range, electric defrosting with brine circuit not filled, electric defrosting with brine temperatures above 115 °C causes the thermal fuse of the safety temperature limiter to blow and requires replacement.
F.723	Pressure loss in the emitter circuit due to leak or air pocket, emitter circuit pressure sensor defective
F.723	Pressure drop in the emitter circuit due to leak or air, emitter circuit pressure sensor defective
F.724	Sensor not connected or sensor input short-circuited
F.724	Sensor not connected or sensor input short-circuited
F.725	Sensor not connected or sensor input short-circuited
F.725	Sensor not connected or sensor input short-circuited
F.726	Compressor overheated, e.g. due to use outside its application limits, maximum ambient temperature for the heat pump of 40°C was exceeded, compressor blocked by mechanical defect, compressor blocked by too high a pressure difference when switching on (> 3 bar)
F.727	The electronic expansion valve is not working normally.
F.728	Low pressure switch defective, fan defective, leak in the refrigerant circuit
F.729	Compressor outlet temperature lower than 0 °C for more than 10 minutes or compressor outlet temperature lower than -10 °C although the heat pump is in its operating range.
F.729	Compressor outlet temperature lower than 0 °C for more than 10 minutes or compressor outlet temperature lower than -10 °C although the heat pump is within its operating range.
F.730	Low pressure switch input not bridged (X22-8 to X22-11)
F.731	Refrigerant pressure too high. The integrated high pressure switch has activated at 41.5 bar (g), insufficient energy transfer via the relevant condenser
F.731	Refrigerant pressure too high. The integrated high pressure switch has activated at 46 bar (g) or 47 bar (abs), insufficient energy transfer via the relevant condenser
F.731	Refrigerant pressure too high. The integrated high pressure switch in the outdoor unit has activated at 31.5 bar (g) or 32.5 bar (abs), insufficient energy transfer via the condenser
F.731	Refrigerant pressure too high. The integrated high pressure switch (also replace filter) of the outdoor unit has activated, insufficient energy transfer via the condenser
F.731	Refrigerant pressure too high. The integrated high pressure switch (also replace filter) (also replace filter) of the outdoor unit has activated, insufficient energy transfer via the condenser
F.732	The compressor outlet temperature is above 130°C: application limits exceeded, EEV not functioning or not opening correctly, amount of refrigerant too low
F.732	The compressor outlet temperature is above 130°C:, application limits exceeded, EEV not functioning, or not opening correctly, amount of refrigerant too low
F.732	Compressor outlet temperature is above 130°C: application limits exceeded, EEV not functioning or not opening correctly, amount of refrigerant too low (frequent defrosting due to very low evaporating temperatures)
F.732	The compressor outlet temperature is above 110°C: application limits exceeded, EEV not functioning or not opening correctly, amount of refrigerant too low (frequent defrosting due to very low evaporating temperatures)
F.732	The compressor outlet temperature is higher than 130 °C: application limits exceeded, EEV not functioning or not opening correctly, amount of refrigerant too low (frequent defrosting due to very low evaporating temperatures)
F.732	The compressor outlet temperature is above 115°C: application limits exceeded, EEV not functioning or not opening correctly, amount of refrigerant too low
F.733	No flow in the ambient circuit (heating mode), energy yield in the ambient circuit (heating mode) or emitter circuit (cooling mode) too low
F.733	No flow in the ambient circuit (heating mode), energy yield in the ambient circuit (heating mode) or emitter circuit (cooling mode) too low
F.733	Air volume flow through the heat exchanger of the outdoor unit (heating mode) too low, causing too low an energy input into the ambient circuit (heating mode) or emitter circuit (cooling mode), amount of refrigerant too low
F.733	Air volume flow through the heat exchanger of the outdoor unit (heating mode) too small, causing too low an energy input into the ambient circuit (heating mode) or emitter circuit (cooling mode), too little refrigerant
F.733	No flow in the ambient circuit (heating mode), energy yield in the ambient circuit (heating mode) or emitter circuit (cooling mode) too low
F.734	Temperature in the heating circuit too low, outside the operating range, amount of refrigerant too low
F.734	Temperature in the heating circuit too low, outside the operating range, amount of refrigerant too low
F.734	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too low for compressor operation, amount of refrigerant too low
F.735	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too high for compressor operation, supply of external heat into the ambient circuit
F.735	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too high for compressor operation, supply of external heat into the ambient circuit too high due to increased fan speed
F.735	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too high for compressor operation, supply of external heat into the ambient circuit too high due to increased fan speed
F.735	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too high for compressor operation, supply of external heat into the ambient circuit too high due to increased fan speed
F.735	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too high for compressor operation, supply of external heat into the ambient circuit
F.737	Temperature in the emitter circuit (heating mode) or ambient circuit (cooling mode) too high for compressor operation, supply of external heat into the ambient circuit, refrigerant circuit overfilled, flow in the emitter circuit too low

Order parts for your Vaillant heat pump

Vaillant parts are available from Instalpunt; shipping to EU countries from €17.95 (€24.95 for more distant countries), usually 3–5 working days.

Parts by Vaillant series: ecoTEC plus · ecoTEC pro.

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Frequently asked questions about Vaillant faults

What does a fault on a Vaillant 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 Vaillant means by it.

How do I reset my Vaillant heat pump?

The reset button is on the control panel of your Vaillant 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 a Vaillant 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 Vaillant?

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.