poor or no suction dyson dc04 absolute?

my partner lent our vacuum to the chimney sweep thinking he would just vac up a small amount of dust BUT he used it to vac up all the soot out of the fireplace,now it has virtually no suction & the wash clean filter blackens every time it's washed & put back, there are no apparent blockages but am baffled as to the cause, Any help would be great, Thanks