ariston microgenius combi MFFI 23 trips overheat every day???

hi all.
as the title says, my ariston microgenius combi trips out 3 times a day,
it is around 5 years old.
it is more apparent with the heating going constantly. from day one, but the engineer says that he has set it on the upper limit, to maximise hot water, so occasionally, it will trip, due to water temp. it only happened about once a fortnight, so wasnt a big issue. now it is though.
it generally trips after hot water is turned off, or heating cutting in and out. it can do it while in the shower though!
does anyone know if there is an adjustment that i can do myself or another idea?

any advice much appreciated.
thank you for looking.
tony