Shush

As you already know, the letters sh form the sound <sch>, like with the words ship, fashion and fish. But there are a few occasions, when other letter combinations can also have a <sch> sound. Look at the examples below.

SU: sugar, usually

SI in –sion endings: occasionally, passion

SCI in –scious endings: delicious, unconscious

CI: conscience, electrician, especially,

Careful::

TI sounds like <sch> in…

–tious  endings, such as ambitious and rambunctious

and –tion endings, such as ambition and imagination.

Except TI sounds like <ch> in –ction endings, 
such as fraction and satisfaction.

However, CH sounds like a <sch> in machine.