Select a fault code

The burner has failed to ignite. This can be caused by low gas pressure, a faulty ignition electrode, or a blocked condensate pipe in cold weather.

The system water pressure has dropped below 0.5 bar. This is one of the most common Vaillant faults and is usually easy to resolve.

The difference between the flow and return temperature sensors is outside the expected range. This can indicate poor circulation or a heat exchanger issue.

The flow water temperature is rising too quickly, which could indicate a circulation fault or a failing pump.

The flue gas temperature has exceeded the safe limit. This may indicate a blockage or a flue system fault.

The ionisation sensor is detecting a fault with flame detection. The sensor may be dirty or faulty.

The boiler has attempted to light but failed to detect a flame. Low gas pressure or a faulty gas valve are common causes.

The flame went out unexpectedly during operation. This can be caused by a brief gas supply interruption or a fluctuating gas pressure.

The fan is not running at the correct speed. Safe combustion is not possible.

The gas pressure at the boiler is insufficient for correct operation.

A fault has been detected on the gas valve relay. The gas valve cannot be safely operated.

The gas valve safety relay has detected a fault. This is a serious fault that prevents safe gas control.

The boiler's internal memory (EEPROM) has a fault. Settings or fault history may be corrupted.

The water pressure sensor has failed or is reading incorrectly.

System pressure exceeds the safe operating limit (above 3 bar). Over-pressurisation can damage components.

The boiler has not detected a pressure change when the pump starts, suggesting a pump fault, blocked system, or faulty pressure sensor.

The condensate pump has reported a fault. If the condensate cannot drain, the boiler will shut down.

The mains voltage supply to the boiler is too low for safe operation.