Okay I got the HT-RT4 5.1 surround sound system a few weeks ago and it worked great with my 6/7 year old Bravia

I got a new Sony TV the other day KD55XG8505, I have it connected to the ARC HDMI input and the sound does work, however the sound system keeps dropping out of the bravia sync device list

the old TV if I turned up the volume with the TV remote, the soundbar volume went up

Now the new TV occasionally does it but just stops working after a few hours, then randomly starts working

Any idea why it is doing this? I have control set to on in the HDMI setting on the soundbar and as I say it worked on the other TV but is intermittent with this one. I dont want to have ANOTHER remote just to turn volume up and down

thanks