Ferroli Optimax HE 38C No CH and HW switching on/off?

The boiler will sit waiting for HW demand, will supply HW mostly but sometimes display just goes off (so does HW), then display comes back on, other times the HW supply will be fine. CH not coming on at all no matter what I do with the timeclock. Reset it, saw t5 flashing on startup, otherwise no error codes displayed. It's erratic, will for no apparent reason reboot itself and go through the FH purging phase over and over. This boiler was only fitted yesterday and has never worked correctly. Anyone have any idea, Ferroli are shut today...