We have just purchased a new house. We turned the oil fired central heating on, all radiators but 2 are working in the house. I've bleed them but to no avail. They are both downstairs, although 2 other radiators downstairs are working. What could be the problem?

I believe you still have air in the line or the radiators are valved off by a zone valve or a hand valve located in the suooly line.