Do we have any washing machine gurus here ?

Our ~15 year old Zanussi washing machine is developed an odd fault. It fails to rinse properly.

It fills, washes, empties, rinses, spins; but at the end of all of that there are still soap suds in the machine. If I run the rinse cycle a few more times the soap is visibly done, but I don’t know whether it really is rinsed at that point.

I’ve checked the filter (was a bit gunky, but not bad). I’m at a loss as to what to look at, we don’t really want a new machine, this is the first fault this one has ever had.

My Googlefu is failing me on this one.

This is the troubleshooting section of the manual for our machine, it has nothing to help on failing to rinse:

https://www.manualslib.com/manual/199490/Zanussi-Iz-12.html?page=19#manual