Banging Condensing Boiler

[pepsicola]

Hi all, We have a problem. Our 3 yr old Ferroli Optimax 25c condensing combination bolier has started to make banging noises within the last 48 hours. It is wall mounted in the loft with the condensate outlet connection leading to the outside gutter. The boiler has always worked great up until now. Last night we noticed that the outlet was blocked by ice, my husband unblocked the pipe and disconected it putting a bucket under the boiler to catch the waste. The heating has been on all day today with no banging but has now just started again. Why? Is there more to it than just the frozen outlet pipe?
Any advice apreciated.

 

[wnjswozo]

check con trap,if poss,put warm water throu inner flue pipe,may be difficult with boiler in loft