Can a tv go on the wall with back boiler and gas fire?

ume you mean above the fire as this sits on the outer wall of the chimney ? Yes. At your own risk! There is no regulation against this but the heat from the fire may not do the TV too many favours! Obviously don't drill the fixings too deep through into the chimney opening. If you don't use the gas fire, the majority of heat from the back boiler alone would get transferred into the heat exchanger and rise up the flue so don't think you would get heat damage from that!