Bosch VarioPerfect No start - Start/Reload light flashing

Hi folks

Thanks in advance if you can assist me, I've tried the obvious things but can't see any indication in the manuals what's going on here...

Brief history - machine struggling to empty, bought and installed replacement pump. Confirmed that old pump was packed tight with scum and all sorts of mess which would explain why it was struggling to empty. Cleaned it out for what it's worth, but new pump already installed at this stage.

Put machine back on its feet, and now it won't start a cycle at all. When you press Start, the Start / Reload light just flashes steady. Does anyone know what this is trying to tell me? I suspected maybe I damaged the door catch when I put the machine on its side, as I didn't brace the drum or anything, but it's working fine. Machine seems to recognise that the door is closed but it won't go. Also confirmed water pressure is OK. Reinstalled old pump in case new one was duff, to no avail. Also did Bosch fault reset procedure.

Model is a Bosch WAK28261GB/11, about 18 months old.