1930s house with no ground in wiring. Electrician installed AFCI breakers on all circuits with water. I.e., kitchen, bathrooms etc. Upstairs bath would intermittently trip for no apparent reason. Electrician said it could be faulty GFCI outlet and installed new. Nope! Then said could be older electric toothbrush? Got rid of that. Did seem to stop for a few weeks. Then in the last two weeks, it has started tripping (some of the time) when you turn on the shower and engage the tub to shower diverter. Not every time but trips as soon as you pull the diverter. No time for any steam to build up. And trips even if nothing is in use on the circuit. Which is three overhead lights and 4 or 5 outlets. Nothing but lamps and night light on those outlets. Now a bit leary of showering in my lovely cast IRON tub! Help!