my water is gone cold the boiler tries to lite ?

hiy all i,m john i have a valiant boiler i ,ve had 2 radiators removed now i dont have any hot water the boiler tries to lite but has somekinda restriction water pressure is ok but no hot water how do i bleed the system? i hear a gurgling noise in the boiler the green and amber lite come on at start then the amber lite goes off and green lite flashes and stays on i get a jet of hot water for few seconds the it goes off and water goes cold again