Thanks for following up John - that is interesting to see. From other, older threads it looks like there were some issues with early machines that led to the change.
Pleased to say I am back up and running, although I could only find 10A rated units that fitted in stock, so have gone with that for now and changed the config on the machine to enable sequential heating which hopefully means that is completely safe.
I will follow up with ACS to see if it is simple to retrofit the new design in place of the old.
Thanks again everyone for your help and advice - much appreciated.