This is a fault we come across frequently and affects most Vaillant boilers (especially earlier EcoTEC boilers). F.75 error means that the electronic pressure sensor has been unable to detect a rise in pressure when the boiler pump has activated (assuming the pump is operating correctly). This is a relatively simple problem for an experienced heating engineer to solve, and usually doesn't require any parts to be fitted. There are preventative measure that can be taken to reduce the likelihood of this fault occurring in the future that we can advise you of. The electronic pressure sensor is effectively a safety device that prevents the boiler from firing up if there is insufficient flow in the system. This can be caused by low water pressure or no water in system, blocked sensor, blocked heat exchanger, blocked filter, faulty pump, or debris in other parts of the boiler. After repairing your boiler we may recommend a system flush is carried out to ensure this isn't a common occurrence.
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