help with black dust

[bgr_sarh]

my neighbour had a new heating system installed last year and for a while now she has been getting black dust around her house and keeps getting worse ,its mainly evident on the walls and ceilings around the surface mounted radiator pipes that run vertical up the wall but is slowly coating the whole house,the house is fairly modern ,about 20 years old,there is and has never been any coal or gas fires in the property and the only form of heating are radiators fuelled from a condensate boiler which is constantly on about 20 c as she is elderly,there is no chimney ,no flues except from the boiler which vented directly through the wall to outside,no other air flow systems or anything that vents or circulates air ,we live in a cul de sac so theres no issues with pollution and no one burning anything nearby,she only burns the odd candle now and then and doesnt smoke at all,heating system has been checked by landlords gas engineers and even the fire brigade have had a look around the house,i live next door and dont have any traces of black sooty deposits anywhere