Neff S5456X2GB13 not completing cycle: display shows 1 minute remaining

I have a Neff S5456X2GB13 dishwasher that fails to complete the wash cycle. If I open the door the display shows 1 minute remaining but the machine doesn’t give its usual beep to tell me that the cycle is finished. If I then reset it and close the door, the machine runs for a couple of minutes and then does beep to tell me it’s finished.

Initially I thought it was a ‘not heating the water’ problem so I removed the control board, found one of the connections on relay K1 had a burn mark, cleaned and resoldered the connection and reassembled it. This seems to have fixed the heating issue, as I can open the door 10 minutes into a wash cycle and the water is hot.

I think the machine is making a slight ‘groaning’ sound, almost as if the drain pump is struggling, but the machine does drain: when it’s stuck on 1 minute remaining it has already emptied the water out.

Things I’ve checked so far:

• cleaned the filters
• impeller can spin freely
• control board for visible signs of trouble

The machine is getting on a bit (at least 12 years old I think) so I’m prepared to replace it if necessary. But if it’s a relatively easy fix I’d like to keep it going a bit longer if possible.

Does anyone have any ideas what further troubleshooting steps I should take?