Thanks
I have now sorted my dishwasher. For anyone interested who has had the same symptoms, this is the story.
Bosch model smv69t20gb/57 built in Ecosilence dishwasher
Dishwasher stopped with dirty water in the bottom. Flashing check water and rinse aid. Checked and cleaned inlet filter. Cleaned out bowl and filters. Removed and checked sump drainage pump. It had consistent resistance between the three connections. Suspected that flashing lights were some Bosch error code. Phoned Bosch and weedled out of them that it was an interface problem. A lot of searching on the Internet for people with similar problems. Removed and inspected the circuit in the door, no signs of any component failure. Removed the control module lower right hand side of m/c. Black mark on case, one IC completely blown. I typed the numbers on the module into Google and got website that sold used parts but didn't have any. Other parts places sold part "not programmed", they told me I had to get a Bosch "Engineer" to programme it. Phoned Bosch. Eventually they agreed that they would sell me a preprogrammed control module but it "had to go to Germany". Mysteriously it arrived 2 days later. It was not the same long number as the original.
Plugged the new one in using the harnesses for the old one. Switched on. Nothing. Heart sank. Then I realised that the machine was out so the display was off as the door was closed. Phew. Started it, ran pre rinse. Check water light came on ( continuously this time) with beeping. Left it running. When it finished, error code E11. Not in the list. Phoned Bosch again. They said it was water system error. Internet said thermistor. Thought it might be flowmeter reed switch after Internet search. Ordered one. Went back and checked the connections to the control module. Some were not fully seated. Retried. Bingo. Cancelled order for reed switch.
Did a little jig in the kitchen as all this took quite a few days to resolve. My rate as a dishwasher technician is in pennies per hour.
Helpful notes
1) it is helpful to know what is supposed to happen in order to diagnose problems, watching the side panel water tank filling and emptying.
2) pictures of electrical connections before taking off are invaluable.
3) the connections harness for the control module doesn't on its own give a good connection, each connector needs to be pushed down.
4) persist with Bosch, but be polite, they want you to call out a technician. I threatened to write to complain that they were effectively forcing you to call out their technician by not selling a programmed module.
5) Error codes are misleading sometimes.
Regards David