Biasi Parva lock out

[Sicknote614]

Hello all, can anyone suggest the cause of my boiler fault. I have a Biasi Parva boiler. Lock out lamp came on, so I checked the CH pressure it's 1.3 bar also checked the condensate pipe this is clear. So reset the boiler and had normal operation until this morning. The reset was on again. If I only use the hot water the boiler won't reset, but the water will be hot then cold then hot then cold etc. I can hear the fan and I see the ignition electrodes working in the window. The 3 fault indicating lamps show the 2 outer flashing at the normal speed (green) and the centre lamp on steady (red.)
If the job is relatively easy I am willing to give it a try.

Thanks.