3-4 months ago he flushed it and had no problems since - im pretty sure its bled.
check your thermostat. boil water and pour it into a container big enough to hold a thermostat. throw the thermostat into it then watch if it opens up. it should open up around 3-4mm. if it doesnt then its shagged.
you dont need to take the radiator out to flush it, just disconnect the hoses and run water through it.
i read that you flushed your radiator, but did you flush your engine?
you can do it 2 ways;
1. disconnect the radiator hoses that connect to the radiator. run a high pressure water through the top hose for around 30sec. then run water through the bottom hose for 30 sec. its important you do it both ways. personally, i like to disconnect the heater hoses and flush that separately.
2. drain the water (little plug on the LHS of radiator), fill it up with water again, run the engine with a bit of revs for around 20sec (keep an eye on temps), then flush again. keep doing this till the water comes out clean.