Thanks for the suggestions - mains disconnected had no effect. Yes there is a tamper output from the ESP but it is too old to have had the facility to view it. here is an LCD display but very difficult to get to that part of the roof space. Less nimble than I was 12 years ago and need to get above and below central heating pipes through a very narrow opening. I have a couple of ideas, I can switch off the brush bar motor on the Dyson and try it that way and remove the ESP from the tamper loop. I didn't mention that this only happens once, you can vacuum again in the same room and it doesn't happen again.