Thanks for the replies, I have turned the heating on with only one rad open, and have done this in turn with all three - they just get warm.
After paying for the boiler I cant even afford the gas to run it.
Looks like Im taking the radiators off one by one and cleaning, very difficult to...
I dont think the system was flushed, but the plumber has been back since and balanced the rads. This didn't work so Ive been turning radiators on and off left right and centre.
The two rads that do get warm are no where near as hot as the radiators in the rest of the house...
We've had a new boiler fitted, all works fine except three downstairs radiators. One remains cold at all times, the other two will warm up only when all other radiators in the house are turned off and then only the top will warm whilst the bottom remains cold.
The system has been bled...