Indesit dishwasher DIFP 18B1 error

Hi, have an Indesit Dishwasher DIFP 18B1 which doesn’t always start properly.
You can hear the motor start, but then it stops and the green light flashes and shows a 5 on the display. I can’t find this as an error code anywhere.
I have to switch it off, then try again. Sometimes it works, sometimes it doesn’t, (most of the time it doesn’t). There is no difference in what I do to it, just sometimes will work.
I had a plumber out to look at it a year or so ago, and of course it worked first time when he was here. He couldn’t find anything wrong.
Since then it is getting worse, I’d say it’s around 1 in 6 that it will actually work and wash my dishes.
Can anyone help?