TDS lists error code “A” as a fill problem. A4 is not listed. As you have stated that the machine does fill, this may be related to water level control – ie machine not sensing water level correctly. This is probably related to the fill matrix on the side of the machine collecting sludge and is a singularly awkward problem to resolve.
An engineer may well be the best option. Check “Repairs@” for an engineer in your area, or pop up your postcode in here and someone should pick up on it.
Regards,
Penguin45.