triton ivory shower not heating?

with power and pressure to unit there is no hot water
on setting one even with red temp turn knob up full
and on setting two ( second kilowatt ) there is only
tepid warm temp even with temp knob fully turned
to maximum so shower is really always almost cold.
it was working well upto a few weeks ago and went
faulty for no apparent reason. help please as i cant use
baths easily.