Our boiler is under 3 years old and making a high pitched whining noise after using hot water which carries on until hot water is run off again. Then tap turned off and noise starts again. Eventually, the noise does stop, but after perhaps half an hour or more. Maybe pump, or diverter valve at fault? Has anyone had similar experience? Moved in three weeks ago and it's driving us mad.Can't get hold of Sime, are they still operating? Can anyone help please?