Can anyone suggest a method of cleaning the sealant used on UPVC windows?

In our sun porch it is starting to go black in places, particularly in the corners, and I have tried several methods of cleaning this with no success. 'Assuming you've tried vinegar, which can remove lighter stains, dilute two parts warm water to one part chlorine bleach,' says cleaning guru Stephanie Zia. 'Apply to the stain, leave for 15 minutes, then rinse well. If - and only if - the stain appears lighter, repeat until it has gone. You might have to keep at it over days, even weeks. 'For faster results try proprietary sprays such as Astonish Mould & Mildew Remover (£1.50, from supermarkets) or HG Hagesan Mould Spray (£4.95, from homecareessentials.co.uk, 01733 241960), but again don't give up too soon and be prepared to reapply if necessary. Wear rubber gloves, follow manufacturers' instructions and rinse thoroughly each time, especially between applications of bleach and any other product. 'If all else fails, get a handyman to cut out the marks and reseal.' Why are our radiators ...  more