you can use :contains to filter based on text content of an element, but note that it will return partial matches.
So :contains('Vaillant 835')will return :contains('Vaillant 835') and :contains('Vaillant 8356')
jQuery("#select_Boiler option:contains('Vaillant 835')").remove();
If you want to filter for equal you need to do a manual filter like
jQuery("#select_Boiler option").filter(function() { return $.trim($(this).text()) == 'Vaillant 835' }).remove();
