if it is a combi bolier sometimes if the pressure is to low it cuts out.You could try all the upstairs radiators to see if they need bleeding. if they do then re-try the boiler after doing this, check the pressure gauge it should read between 1.5 and 2.0 bar. if the boiler doesnt re-light under normal operating procedures then wait a while for the pressure to build up again.
lee
June 2008