Potterton Netaheat EP 2000?

I have a Potterton Netaheat EP2000.
Recently the power in my whole flat cut itself off following the start up of the boiler. An electrician confirmed that the pump had burnt itself out and tripped the fuse board.
I have replaced the pump, flushed out the system, filled the header tank with a cleaning solution and I still cannot get the boiler to work.
When the boiler now comes on it ignites and burns for about 8 minutes and then cuts out. You can hear a fluttering noise which gets more audible just before the boiler cuts out. The boiler will fire periodically but always does the same thing...............can anyone help me?