Strange white powder on back boiler

[Boilerman2]

The white residue you describe sounds like the result of dust burning during the combustion process it is not un-common to see this type of white residue particullarly on open flue appliance heat exchangers
it is nothing to worry about - quite normal!!

 

[Onetap]

I think OneTap was making a joke, Alex.

I even put a smiley on!

It might be acidic condensation reacting with a metal flue liner (aluminium or zinc/galvanized steel?). The flue gas temperature should be high enough to prevent condensation.

 

[alexh75]

I think OneTap was making a joke, Alex.

I even put a smiley on!

It might be acidic condensation reacting with a metal flue liner (aluminium or zinc/galvanized steel?). The flue gas temperature should be high enough to prevent condensation.

i know....can't believe i missed that!
i suggested condensation but he ruled that out for the reason you mentioned.....

 

[gaswizzard]

Is chimney on an external wall?

 

[alexh75]

Is chimney on an external wall?

no, semi detached bungalow, on separating wall
Alex