Worcester Highflow 400 RSF?

looks like we may be without heating and hot water for xmas. Heating stopped working at 8.30pm last night, jiggled some of the wires and system fired up - left heating on due to the cold weather or to get up this morning anf no heating again. Bled the pump and hay presto heat again - later on this afternoon both heating and hot water stopped. Any ideas?

john
December 2009