Tip some water down the flue(the inner part/where the steam/flumes/heat comes out outside). the water should run throught the boiler and out of the condestate pipe(white plactic pipe on the botton of the bottom) If it doesn't you have another blockage. A leaking condenstate pipe can also leak fumes, so get the leak sorted as some as you can.
LTGF
August 2008