how can i fix GREENSTAR 24i junior / 28i junior combi boiler?

just bled radiators for first time. Now all radiators have gone cold but heating is still on. Dont know what to do next. Dial behind front panel at zero. Can only see one valve with a row of pipes below boiler.
Dont have any real help in manual for the GREENSTAR 24i junoir / 28i junior combi boiler system.