HELP - Thorn EMI Apollo Fanfare boiler - hot water but radiators freezing!!?

I have a Thorn EMI Apollo Fanfare boiler. The pilot light is on, the hot water is on.. But the radiators are not coming on. The boiler is making quite a loud noise but I just thought the noise was because it's so old. How can I get my radiators to heat up?
I'v checked everything and it's all set correctly. But I have no heat... Please help.. is sooooooooo cold!!!!
Any ideas what's wrong??
Ta!