loss of channels

Hi there, I was at my parents today as my mother said she had no TV, the upstairs bedroom tv had no signal, did a scan and I got 'no signal' the down stairs had most of the ITV channels along with 4, 5 E4 etc but no BBC channels, did a scan there and the ITV channels etc came up but no data for BBC and other channels lost. Its a loft ariel with a distribution amplifier checked all the leads everything OK and on, I'm on the same transmitter and have all channels so I;m at a loss as how to fix this can anyone help.

Our transmitter is Durris

Thanks in advance