Brilliant mate, I am finally on the right track then lol
After having all of the radiators on for 10 minutes I have noticed a considerable drop in temperature of the warm parts of the "faulty" radiator. I am guessing that the balancing does need looking at now so have just turned all of the heating off and I am going to let the rads cool down, then me and my wife are going to try and figure out the order of the radiators.
Then tomorrow I will get the radiator off and flush it and balance the radiators!
If I have missed anything please let me know