My wife owns a flat that she's been renting out for the last 6 months. At the handover between one tenant and the next, she's found mould behind just one radiator in the flat. We're curious to know why it's there, and what we can do about it.
There isn't any mould anywhere else in the flat. The radiator is in the smallest bedroom, which might have been left unheated. The radiator is on an external wall, which might therefore have been quite cold. The wall itself is (I think) plasterboard mounted onto the external wall, with a void between the two. The plumbing runs through that void. There's a hole in the plasterboard, behind, roughly, the centre of the radiator, through which the plumbing is fed to the radiator. The other radiators in the flat have the same arrangement, but they all have a metal plate with small holes covering the larger hole in the plasterboard, and the plumbing is fed through the small holes. The mould seems to be centred on the large hole in the plasterboard, though it's spread outwards and downwards more than it's spread upwards.
Is it possible that the missing plate is letting more cold air onto the room-facing surface of the plasterboard, causing enough condensation for the mould? If so, we should probably get a plate installed? I guess it would be sensible to recommend that that radiator is left on, at least on a low setting, and at least in cold weather? Any other recommendations or suggestions?
Thanks in advance,
Simon.