Baxi Bermuda back boiler - metalic knocking noise (ed.)

[Michal Sawada]

Hello guys.
We have Baxi Bermuda back boiler and from few day when fireing up CH or HW there is metalic knocking noise like on the metal sheet for about 1-2 min then stops and same again when fireing back, I have took fireplace cover off and can tell it's coming from heat exchanger, any help would be much appreciated.

 

[CBW]

Any other issues with system?

 

[Michal Sawada]

No not really all works fine both ch and hw

 

[ianmcd]

One of the most reliable gas boilers ever made, sorry your post doesnt make much sense can you elaborate, pics are best as what you call parts of the boiler might not be correct

 

[Michal Sawada]

Right will try explain better,
When CH or HW fires up for about 2 min. There is a knocking metalic (like bending metalic sheet or knocking on metalic sheet) sound coming from heat exchanger what's sits above burner and then stops untill fire goes off and fires back up then starts again. Unfortunately unable to upload recorded sound. All works fine CH & HW no other issues. Just wondering if anyone had an experience with that kind of sound and what's the solution i.e. Draining and adding cleaner fluid.
Thanks in advance