Thats' the air outlet hole that stops the vacuum from over heating. If the vacuum isn't working properly then it will be the filters that need a thorough clean. Dismantle all the filters and give them a wash - the top cylindrical paper filter is washable and you can dry it in a low temp electric dryer by placing it into a pillow case with a tea towel to stop it bouncing off the walls of the dryer. The hole at the back shouldn't be covered over however.
ukvacfan
September 2008
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