My Janome packed up a while ago and I have been borrowing Tina's ever since. I eventually got round to finding out what the problem was by paying a visit to the local specialists at 181 Deptford High Street. Not only was the foot pedal faulty "it's a standard problem on this model, madam", but I had speared the rotary bobbin holder when unblocking the machine. There were some tiny holes in the hard plastic and they were catching on the thread, which meant I had to stop and start all the time.
After a lot of hard bargaining about part exchange values, I traded in the Janome and bought a Bernina instead. Oh the joys of bombproof metal bobbin cases! Of course the machine is completely different and it takes a while to figure out how to set it up, but once it is running it is a delight. It seems to purr along without making any effort and has the build quality of a bank vault door. They may make them near Chiang Mai in Thailand now, but there is something very solidly Swiss about Berninas.