Vaillant boiler fault & error codes

When you realise your Vaillant boiler isn't operating as it should, the system interface will show an error code. These codes aid engineers when they’re working to identify boiler issues, particularly when those problems aren't immediately obvious.

Due to the variety of components within a boiler, there are many potential problems that your boiler may experience. In order to streamline the process, we'll go over all of the most typical error codes for the most common Vaillant boiler models here so you can make sure any issues are resolved as soon as possible.

Vaillant boiler fault & error codes by boiler model

• Vaillant ecoTEC Plus Combi error codes
• Vaillant ecoTEC Pro Combi error codes
• Vaillant ecoFIT Pure Combi error codes
• Vaillant ecoTEC Exclusive Green iQ Combi error codes
• Vaillant ecoTEC Plus Regular error codes
• Vaillant ecoFIT Pure Regular error codes

Vaillant ecoTEC Plus 1 Combi error codes

The Vaillant ecoTEC Plus Combi Boilers offer a great blend of energy efficiency and dependability for home heating. 

With their compact design, these combi boilers help you get the most out of the space you’ve got. The clue is in the name: this model prioritises environmental sustainability, making it a conscientious choice when it comes to heating your home.

Error Code	Issue
Con	There is a communication error occurring between your boiler's PCB (inside the electronics box) and the display. The PCB may need to be replaced.
F.00	The flow temperature sensor is defective or not connected.
F.01	The return temperature sensor is defective or not connected.
F.02	The shift-load cylinder temperature sensor is defective or not connected.
F.03	Shift-load cylinder temperature sensor is defective or not connected.
F.10	The flow temperature sensor is experiencing a defect or a short circuit.
F.12	Cylinder charging sensor defective or has short-circuited.
F.13 (safety switch-off)	The warm start sensor/cylinder temperature sensor is either not connecting or defective.
F.20	Maximum temperature at the flow/return temperature sensor is too high when the safety cutout function is operating.
F.22 (safety switch-off)	The water pressure is too low, or there is either an insufficient quantity of water in the product or none at all.
F.23 (safety switch-off)	The temperature spread is too great, and the water circulation is low.
F.24 (safety switch-off)	The temperature has increased too quickly.
F.25 (safety switch-off)	The flue gas temperature is too high.
F.26	The Gas valve assembly stepper motor is either defective or not connected.
F.27	Monitoring electrode reports an incorrect flame
F.28	Failure during start-up or ignition unsuccessful. The gas pressure monitor or thermal cut-out has been triggered.
F.29	Gas supply interrupted intermittently. Re-ignition failed.
F.32	The fan isn't connected or is experiencing a defect.
F.42	Coding resistor or gas group resistor is causing a short circuit.
F.49	Undervoltage on the eBUS.
F.52	Mass flow sensor is defective or not connected.
F.53	The mass flow through the gas valve assembly is not as required.
F.54	No gas inlet pressure or insufficient gas inlet pressure causes faults when the appliance is used.
F.55	All-gas sensor is defective or has short-circuited.
F.56	Safety shutdown after the CO limit value is exceeded.
F.57	Regulation fault caused by a corroded ignition electrode.
F.61	The gas valve assembly cannot be actuated.
F.62	Delayed switch-off sequence for the gas valve after the flame is extinguished.
F.63	EEPROM is faulty.
F.64	There is a defect with the electronics, safety-relevant sensor, or cable.
F.65	Electronics defective or too hot due to external factors.
F.67	The flame signal is weak/not detected.
F.68	The flame monitor is reporting an unstable flame signal.
F.70	Incorrect/missing Device Specific Number or incorrect/missing coding resistor.
F.71	Flow temperature sensor returns implausible values.
F.72	The temperature difference between the flow and return temperature sensors is too large.
F.73	The water pressure sensor is showing that the water pressure inside your boiler is too low.
F.74	The water pressure sensor is showing that the water pressure inside your boiler is too high.
F.75	Insufficient pressure jump detected when starting the pump.
F.77	No flue non-return flap feedback; condensate pump overflow.
F.78	UK link box is connected without the domestic hot water temperature sensor being bridged.
F.80	Inlet temperature sensor defective or not connected.
F.81	Cylinder is not fully charged after the specified time.
F.82	External current anode defective or not connected.
F.83	The temperature difference between the flow and return temperature sensor is too small.
F.84	There is a permanent temperature difference between the flow and return NTC thermistors.
F.85	Flow/return temperature sensors are returning incorrect values.
F.90	Communication with actoSTOR was interrupted.
F.91	Sensor on the actoSTOR is defective.
F.92	The coding resistor on the PCB does not match the gas group that is entered.
F.93	Combustion quality is outside the permitted range.
F.94	Sensors return incorrect values.

Vaillant ecoTEC Pro Combi error codes

Similar to the ecoTEC Plus, the Vaillant ecoTEC Pro Combi Boilers are known for their efficiency, reliability and eco-consciousness. Being a close relative of the ecoTEC Plus, the boiler boasts many of the same features, but the Pro is aimed more at people looking for a simpler, cheaper model.

Error Code	Issue
Communication fault	There is a communication error occurring between your boiler's PCB (inside the electronics box) and the display. The PCB may need to be replaced.
F.00	The flow temperature sensor is defective or not connected.
F.01	The return temperature sensor is defective or not connected.
F.10	The flow temperature sensor is defective or short-circuiting.
F.11	Return temperature sensor defective or has short-circuited.
F.20	Maximum temperature at the flow/return temperature sensor is too high when the safety cutout function is operating using the NTC.
F.22 (safety switch-off)	Water pressure is too low, or there is either an insufficient quantity of water in the product or none at all.
F.23 (safety switch-off)	The temperature spread is too great, and the water circulation is low.
F.24 (safety switch-off)	The temperature has increased too quickly.
F.25 (safety switch-off)	The flue gas temperature is too high.
F.26	The gas valve assembly stepper motor is defective or not connected.
F.27	The monitoring electrode reports an incorrect flame.
F.28	Failure during start-up or ignition unsuccessful. The gas pressure monitor or thermal cut-out has been initiated.
F.29	Gas supply interrupted intermittently. The re-ignition has failed.
F.32	The fan isn't connected or is defective.
F.49	Undervoltage on the eBus.
F.61	The gas valve assembly cannot be actuated.
F.62	Delayed switch-off sequence for the gas valve after the flame is extinguished.
F.63	EEPROM is faulty.
F.64	There is a defect with the electronics, safety-relevant sensor, or cable.
F.65	Electronics defective or too hot due to external factors.
F.67	The flame signal is weak/not detected.
F.68	The flame monitor is reporting an unstable flame signal.
F.70	Incorrect/missing Device Specific Number or incorrect/missing coding resistor.
F.71	Flow temperature sensor returns implausible values.
F.72	The temperature difference between the flow and return temperature sensor is too large.
F.73	The water pressure sensor is showing that the water pressure inside your boiler is too low.
F.74	The water pressure is too high.
F.75	Insufficient pressure jump was detected when starting the pump.
F.77	No flue non-return flap feedback; condensate pump overflow.
F.78	UK link box is connected without the domestic hot water temperature sensor being bridged.
F.83	The temperature difference between the flow and return temperature sensor is too small.
F.84	There is a permanent temperature difference between the flow and return NTC thermistors.
F.85	Flow/return temperature sensors are returning incorrect values.

Vaillant ecoFIT Pure Combi error codes

This cupboard-size boiler is a fantastic option for most homes in the UK.

With a high-performance build and smart controls, this model is a prime choice for homeowners looking for a flexible, lightweight and compact boiler that pulls no punches on performance.

Con	There is a communication error occurring between your boiler's PCB (inside the electronics box) and the display. The PCB may need to be replaced.
F.00	The flow temperature sensor is defective or not connected.
F.01	The return temperature sensor is defective or not connected.
F.10	The flow temperature sensor is defective or short-circuiting.
F.11	The return temperature sensor has short-circuited.
F.12 and F.91	The cylinder temperature sensor has short-circuited.
F.13	The temperature sensor for the domestic hot water cylinder has short-circuited.
F.20	Safety shutdown. The overheating temperature has been reached.
F.22 (safety switch-off)	Water pressure is too low, or there is either an insufficient quantity of water in the product or none at all.
F.23 (safety switch-off)	The temperature spread is too great, and the water circulation is low.
F.24 (safety switch-off)	The temperature has increased too quickly.
F.25 (safety switch-off)	The flue gas temperature is too high.
F.27	The monitoring electrode reports an incorrect flame.
F.28	Boiler ignition fault. Unsuccessful ignition when starting up.
F.29	Flame loss fault.
F.32	Fan frost protection function active. Fan speed outside the tolerance values.
F.49	eBus fault. The voltage is too low.
F.61	The gas valve assembly cannot be actuated.
F.62	Delayed switch-off sequence for the gas valve after the flame is extinguished.
F.63	EEPROM is faulty.
F.64	There is a defect with the electronics, safety-relevant sensor, or cable.
F.65	The electronics temperature is too high.
F.67	The flame signal is weak/not detected.
F.68	The flame monitor is reporting an unstable flame signal.
F.70	Invalid product code (DSN).
F.71	Fault with the flow and return temperature sensor.
F.72	Deviation in the water pressure sensor or return temperature sensor.
F.73	The water pressure sensor is not connected or has short-circuited.
F.74	Electrical problem in the water pressure sensor.
F.75	Pressure sensor fault.
F.76	The safety cut-out in the primary heat exchanger is defective.
F.77	Defective flue non-return flap
F.78	Interruption to DHW outlet sensor at external control.
F.83	Dry fire.
F.84	Flow/return temperature sensor fault.
F.85	Temperature sensor fault.
F.86	Underfloor heating contact fault
F.87	Fault with electrodes.
F.88	Fault with the gas valve.
F.89	Fault with the pump.
F.97	Defective main PCB.

Vaillant ecoTEC Exclusive Green iQ Combi error codes

One of the top boilers in the Vaillant range, this model promises performance, control and efficiency. It's kitted out with smart controls, boasts eco-efficiency and is made from 85% recyclable materials. 

The Vaillant ecoTEC Exclusive Green iQ Combi is a fantastic option for homeowners looking for something that’s at the cutting edge of home heating solutions.

Error code	Issue
F.00	Flow temperature sensor defective or not connected.
F.01	The return temperature sensor is defective or not connected.
F.02	DHW outlet sensor interrupted.
F.03	Cylinder sensor interrupted.
F.10	The flow sensor has short-circuited.
F.11	The return sensor has short-circuited.
F.12	DHW outlet sensor has short-circuited.
F.13	Cylinder sensor has short-circuited.
F.20	Incorrect earth connection between the cable harness and product.
F.22 (safety switch-off)	The boiler’s water pressure is too low.
F.23	Temperature spread too large.
F.24	Temperature increasing too fast.
F.25	Flue temperature is too high.
F.26	The fuel valve is not working.
F.27	Flame simulation.
F.28	Ignition unsuccessful. The gas meter is defective.
F.29	Ignition unsuccessful. The gas supply has stopped.
F.32	Faulty fan.
F.33	Pressure switch fault.
F.35	Air/flue gas duct fault.
F.42	Coding resistor fault.
F.49	eBUS fault.
F.55	CO sensor fault.
F.56	CO limit exceeded.
F.57	Measuring program fault.
F.61	Fuel valve actuation fault.
F.62	Fuel valve switch-off delay.
F.63	EEPROM fault.
F.64	Electronics/sensor fault.
F.68	The flame signal is weak/not detected.
F.70	Invalid device-specific number.
F.71	Flow sensor fault.
F.72	Flow/return sensor fault.
F.73	Water pressure sensor fault.
F.74	Water pressure sensor fault.
F.75	Water pressure sensor fault.
F.77	No response from flue non-return flap or condensate pump defective.
F.78	UK link box is connected, but the domestic hot water NTC is not bridged.
F.80	actoSTOR inlet sensor fault.
F.81	Cylinder charging pump fault.
F.82	External current anode fault.
F.83	NTC temperature gradient fault.
F.84	Flow and return temperature sensors are returning implausible values.
F.85	NTCs fitted incorrectly.
F.90	Communication fault.
F.94	Vortex and differential pressure fault.

Vaillant ecoTEC Plus Regular error codes

The ecoTEC Plus Regular (aka standard or heat-only) is a popular choice amongst homeowners who want a high-performing, energy-efficient boiler. This is an ideal choice for larger properties with multiple bathrooms and greater hot water requirements.

Error code	Issue
Con	There is a communication error occurring between your boiler's PCB (inside the electronics box) and the display. The PCB may need to be replaced.
F.00	The flow temperature sensor is defective or not connected.
F.01	The return temperature sensor is defective or not connected.
F.10	The flow temperature sensor is defective or short-circuiting.
F.11	The return temperature sensor has short-circuited.
F.12 and F.91	The cylinder temperature sensor has short-circuited.
F.13	The Temperature sensor for the domestic hot water cylinder has short-circuited.
F.20	Safety shutdown. The overheating temperature has been reached.
F.22 (safety switch-off)	Water pressure is too low, or there is either an insufficient quantity of water in the product or none at all.
F.23 (safety switch-off)	The temperature spread is too great, and the water circulation is low.
F.24 (safety switch-off)	The temperature has increased too quickly.
F.25 (safety switch-off)	The flue gas temperature is too high.
F.27	The monitoring electrode reports an incorrect flame.
F.28	Boiler ignition fault. Unsuccessful ignition when starting up.
F.29	Flame loss fault.
F.32	Fan frost protection function active. Fan speed outside the tolerance values.
F.49	eBus fault. The voltage is too low.
F.61	The gas valve assembly cannot be actuated.
F.62	Delayed switch-off sequence for the gas valve after the flame is extinguished.
F.63	EEPROM is faulty.
F.64	There is a defect with the electronics, safety-relevant sensor, or cable.
F.65	The electronics temperature is too high.
F.67	The flame signal is weak/not detected.
F.68	The flame monitor is reporting an unstable flame signal.
F.70	Invalid product code (DSN).
F.71	Fault with the flow and return temperature sensor.
F.72	Deviation in the water pressure sensor or return temperature sensor.
F.73	The water pressure sensor is not connected or has short-circuited.
F.74	Electrical problem in the water pressure sensor.
F.75	Pressure sensor fault.
F.76	The safety cut-out in the primary heat exchanger is defective.
F.77	Defective flue non-return flap
F.78	Interruption to DHW outlet sensor at external control.
F.83	Dry fire.
F.84	Flow/return temperature sensor fault.
F.85	Temperature sensor fault.
F.86	Underfloor heating contact fault
F.87	Fault with electrodes.
F.88	Fault with the gas valve.
F.89	Fault with the pump.
F.97	Defective main PCB.

Vaillant ecoFIT Pure Regular error codes

Despite their straightforward design, these boilers use modern technology to maintain competitive performance. They’re a solid option for homeowners looking for a boiler that is both cost-effective and dependable.

Error code	Issue
Con	There is a communication error occurring between your boiler's PCB (inside the electronics box) and the display. The PCB may need to be replaced.
F.00	The flow temperature sensor is defective or not connected.
F.01	The return temperature sensor is defective or not connected.
F.10	The flow temperature sensor is defective or short-circuiting.
F.11	The return temperature sensor has short-circuited.
F.13	The temperature sensor for the domestic hot water cylinder has short-circuited.
F.22 (safety switch-off)	Water pressure is too low, or there is either an insufficient quantity of water in the product or none at all.
F.23 (safety switch-off)	The temperature spread is too great, and the water circulation is low.
F.24 (safety switch-off)	The temperature has increased too quickly.
F.25 (safety switch-off)	The flue gas temperature is too high.
F.27	The monitoring electrode reports an incorrect flame.
F.28	Boiler ignition fault. Unsuccessful ignition when starting up.
F.29	Flame loss fault.
F.32	Fan frost protection function active. Fan speed outside the tolerance values.
F.49	eBus fault. The voltage is too low.
F.61	The gas valve assembly cannot be actuated.
F.62	Delayed switch-off sequence for the gas valve after the flame is extinguished.
F.63	EEPROM is faulty.
F.64	There is a defect with the electronics, safety-relevant sensor, or cable.
F.65	The electronics temperature is too high.
F.67	The flame signal is weak/not detected.
F.68	The flame monitor is reporting an unstable flame signal.
F.70	Invalid product code (DSN).
F.71	Fault with the flow and return temperature sensor.
F.72	Deviation in the water pressure sensor or return temperature sensor.
F.73	The water pressure sensor is not connected or has short-circuited.
F.74	Electrical problem in the water pressure sensor.
F.75	Pressure sensor fault.
F.76	The safety cut-out in the primary heat exchanger is defective.
F.77	Defective flue non-return flap
F.83	Dry fire.
F.84	Flow/return temperature sensor fault.
F.85	Temperature sensor fault.
F.87	Fault with electrodes.
F.88	Fault with the gas valve.
F.89	Fault with the pump.
F.97	Defective main PCB.

Protect your home’s central heating with BOXT

Luckily, the majority of Vaillant boiler problems are relatively quick and easy for qualified engineers to fix, provided they’re identified promptly. If you suspect that any of the issues mentioned above are to blame for your boiler’s malfunctioning, and the recommended fix isn’t as simple as pressing the reset button, always contact a Gas Safe registered engineer who’ll be able to come and assist you.

For more help, our team of fully qualified boiler engineers works nationwide to make sure your home’s heating system doesn’t leave you high and dry. Book your boiler repair with a BOXT professional online.