Vokera lock out

I have a Vokera combi boiler, fairly old, I'm sorry I do not have the model number as I type this (could it be 92?), my problem is I drained the CH system to replace a leaking radiator, I have now refilled the system, bleeding all the radiators but the system locks out when trying to start it. Its indicating low pressure, the CH system is pressurised to 1 bar. But when trying both hot water and CH it locks out indicating low pressure,red light comes on, do I need to bleed the pump or something? I cannot hear the pump working, everything was working OK prior to draining system. any help would be much appreciated.

Thanks

The model is a minimum requirement to get any accurate help.

Could be a low pressure switch problem.

What does the boiler look like.

pump reqs venting.auto air bleed not working.try checking