my Vokera maxin24e keeps locking out?

I have had replaced so thermostats, diafram, heat exchanger also the have tested gas flow and water, ignition and burner all seem to be ok but this keeps happening:-
SATURDAY 14/02/2009

06.30……C/H ON ONLY / LOCKOUT +PUMP RUNNING / BAR PRESSURE OK
12.00…….C/H ON….TOOK SHOWER AFTER SHOWER LOCKOUT/NO PUMP RUNNING / BAR PRESSURE OK
17.00…….C/H ONLY / LOCKOUT / PUMP RUNNIG / BAR PRESSURE OK
22.15…….TURNED C/H ON …OK / BAR PRESSURE OK

SUNDAY 14/02/2009

07.10……..C/H ON …ALL OK / BAR PRESSURE OK
13.00……..C/H ONLY / LOCKOUT / PUMP RUNNING. / BAR PRESSURE OK
15 45……..C/H ONLY / LOCKOUT NO PUMP RUNNING. / BAR PRESSURE OK
17.05……...C/H ON OK / RAN BATH WATER COLD / LOCKOUT. / BAR PRESSURE OK
20.00 …….C/H ON OK / TURNED KITCHEN TAP ON COLD / LOCKOUT. / BAR PRESSURE OK

MONDAY 16/02/2009

07.00……..C/H ON OK / BAR PRESSURE OK
08.30……..C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK
22.00…….. C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK

TUESDAY 17/02/2009

07.00…….. C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK
08.00……...C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK
12.30……... C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK
16.45……... C/H ON OK / TURNED KITCHEN TAP ON COLD / LOCKOUT. / BAR PRESSURE OK

WEDNESDAY 18.02.2009

07.00………. C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK
16.00………. C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK
17.00………. C/H ONLY LOCKOUT / PUMP RUNNING / BAR PRESSURE OK