Whirlpool ADG 957 dishwasher keeps steaming at end of cycle

Apologies posted in wrong forum originally!!!
Model Whirlpool ADG 957 NGLF
Although I have had to replace various parts over the years I have had over 14 years of very good service from this machine. Recently though it seemed to start washing things at too hot a temperature since older style plastic items which had previously washed fine came out warped and half melted.

I assumed a NTC fault and duly replaced it, but the problem persists. The dishwasher completes the wash cycle normally. However instead of cooling down at the end as it reverts to its standby rinse setting, the water left in the sump continues to boil and gurgle, and if observed with the mesh and filter removed it splashes quite violently. Even if you turn it off and leave it to cool down, when you turn it back on this boil activity starts again. Is this part of a drying cycle gone wrong? I ran the machine in test mode and no faults were apparent. I am at a loss as to what is going on but I don’t want to throw out a machine which is otherwise working very well.

I hope someone can advise.

Cheers
Rob