Analogue pressure switches

These seem to add another layer of complication to fault diagnosis and are difficult to test with the small plugs on them. Siphoning sent one haywire today on Hotpoint w/dryer -the machine filled, agitated, filled, agitated etc until the drum was full. On putting it to drain it emptied, filled 10 seconds, drained,filled etc and wouldnt end the cycle. Simply pulling the pipe from the outlet and setting it on the drain cycle cured it but I couldnt get my head around what was happening especially on the drain cycle. One of our local Hotpoint franchised engineers says that some of the later machines have to be reset by them if the drain filter is removed without unplugging the machine first ,dont know if this is true as I heard it secondhand.