I just like to ask if you would have found this right away. I went to a worcester 24 i yesterday,and the fan was stuck,cleaned it and it went for a while then stuck and we changed it. I stayed and tested h/water and c/heating anyway , today a call " no h/w or c/h". Went back and this had been in since 2001,it was firing and after 1 min cutting off,firing again,off 1 min later,and so on.fan ok,aps,venturi ok,everything looked to be working as it should until after a minute.I was now looking at the flue and it was a vertical flue but when i looked outside it looked ok. I was now upto a hour and he asked "any joy", i told him the truth"im a bit puzzled",id tried a new aps and the same,anyway i told him i was checking the flue and when i did in the loft , i found the air intake was ok , but he had a gap of 4 " that had been left like that since day 1,. How long would you have took ,me 1 1/2 hour's woman moaning saying i should have seen it yesterday,i only charged then £80 to cover the flue ex.