dvd recorder jumping from av2 to tv channel?

Hi.
when i switch on the unit it automatically changes from my tv channel to AV2 now thats fine but after about 10 minutes of the unit being on it the starts jumping between AV2 and tv ...
Please any suggestions how to stop this !
I have checked and re checked several times all me connections and they are fine I have even swapped all my scart leads and still the problem is the same.
is there a way to turn off the auto channel jump, like you can with a sky box ???
this happens whether the unit is just turned on, watching a dvd, watching a recorded program, on time shift or recording a program.
Thanks for your time.