In reply to ericinbristol:
I was told on a previous home with concrete roof tiles and a lot of moss, not to remove the moss as it was not recommended. The surface of tiles would most likely be damaged by pressure washing/ heavy brushing causing future problems and premature replacement. Damage to the tiles was done on the removal of the moss and not the moss itself.
Recently I had a sales person of a roof cleaning company at my door and when I mentioned the above, he responded by saying that they sealed the tiles with paint so there would not be a problem. He skirted around whether the cleaning actually damaged the tiles, but just repeated that they sealed the tiles anyway so it wasn’t a problem. He could get their surveyor to visit and discuss if necessary!!
I did notice on a neighbour’s roof they cleaned and painted that they replaced various tiles after cleaning. Whether they broke them walking on them, by pressure washing or whatever I don’t know.
Anyway, take what you will with that, but makes me think the professional opinion not to remove moss I had years before was more likely to be the best. I’ve never removed any moss in my current roof (except guttering) and not aware of any problems.