Doesn't sound right
Manual may help or contact manufacturer.
https://www.worcester-bosch.co.uk/support/literature/download/release/8716106859/12785&ved=2ahUKEwi-kfO9u7DZAhWTe8AKHYfPDiAQFjAAegQICRAB&usg=AOvVaw2GdpET29jWh7POpTQJ5JXD
Whheehh
February 2018