Boiler seems to be working fine but the heat coming from the radiators has dipped to almost half.

Now all the stupid stuff has been checked, thermostat up to max, all radiators up to max, re lit the boiler and its not turned itself off

the radiators are a little colder at the bottom than at the top so i'm about to bleed the radiators but is there anything else i should be checking before calling in a professional (who'll scratch his butt and charge me £60 for the pleasure of coming to my house)

thanks in advance before i set fire to the dog for more heat

"radiators are a little colder at the bottom than at the top"

probably not air int hem then it's just that they heat up from the top down.

dodgy pump would do it – can you feel it goign?

or the little valve thing that switches between hot water/rads/both coudl be stuck/partially blocked – there's a little manual override on the bottom usually.

cold at bottom hot at top is an idication of poor circulation.

Could be many things, pump, sludge (i hate the way everything is blamed on this), blockage in pipework (usually where the cold feed joins in), a partial air lock in a common part of the system, balancing.

Has it happened suddenly, if so unlikely to be sludge as that would happen gradually.

Try turning all radiators off bar one and see if that works, also try running it on heating only and make sure that no water is being diverted around the hot water cylinder.

Really need more info to give more of an idea. You are not SE based are you?

See if you pump has speed controller on the side Bosch ones nornally do. Whack it up to No.3 and see if that improves anything. You have got 1 bar in your system ( normal combi pressure) although that shouldnt nake too much difference.