How can I fix the fault on my Triton Shower Assembly model no T80i?

My Triton model no T80i does not heat up now, just cold water whatever position I chose and I cannot hear it cutting in and out.Do you hink it could be the THERMASTAT or the Thermal Cutout if so how do I go about getting a replacement part?
Last time theorange light came on got boiling hot then went cold and stayed that way.
Please advise.