call me stupid but errr whats a TOFFO apart from them chewy sweets that come in a red packet.
like others hav said there could be many reasons for you troubles, pump, diverter valve, sludged pipes.
the switch labelled water heater on you hot water tank is the immersion switch, think of it as your emergency back up HW switch.
as for balancing, i wouldnt really worry about this 12 deg differnece, generally you want all the rads to heat up at approx the same time at the same temp.
make a note of the ones that currently get hottest first, then second etc.
go back round and shut the inlet valve (flow) side of all the rads, then open up approx 1/2 to 1 turn.
see how this works, you may then still have to open/close to fine adjust. its a bit of a black art sometimes.lol
also if you want a powerflush done then i can hook you up..