Algae on wall by boiler

[scouse1965]

Hi We have the same problem green alga has appeared on an external wall due the condensation from the boiler flue outlet. Has anybody managed to solve the problem?

 

[JohnD]

photos please.

I wonder if you mean dripping from the flue, or if you mean condensation on the wall arising from steam emitted.

Green algae on the outside wall below the boiler most often has a different cause.

 

[Stadan20]

I bet it's from a filling loop left open