biasi 24s hot water off and on ?

i have a biasi 24s ,i had it for 2 years now ,when i turn the hot tap on it kicks in (the jets fire up then the jets go off) sometimes it stays on enough for a bath then another time its off and on been like this for a week or so heating is fine . i had the plumber out he cleaned the switch it seemed ok then 10 mins later same again ,so he ordered a new switch thing and seemed ok later on same day back to the same hot water off and on but this time the red cut off button is coming on ,so what now anyone help PLEASE