I have a damp problem behind a living room radiator (see images). The plaster has become soft in patches. On the other side of the wall is the kitchen and in particular immediately behind the patches is a dishwasher. As it is in a fitted kitchen I'm reluctant to take out the dishwasher to see whether the damp is behind it and whether it's caused through a leak or just condensation.
I'd appreciate any advice as to next steps and potential remedies.