RF is UHF, the output doesn't change, but the channel might have reset to the default channel. Check the TV tuning.
The output of the scart socket can be changed from standard to RGB, which is better quality. Howver, if your VCR or TV doesn't support RGB input, you'll get a blue screen instead of a picture (not all scart sockets support RGB, check your VCR and TV handbooks). IIRC, only one of the Sky sockets changes to RGB, check the handbook for which.