Triton T90si electric shower temperature stuck on hot.

that would be right
temperature controls ( thermostats) have an upper and lower temperature range in which they operate and that can be 5-10 degrees
what you need is a cold water supply into the shower so that you can set the shower exit water properly

Sorry to ask but are you gradually increasing the water temperature from cold to medium to hotter. Let it run a little while hot and cold mixes to give you your desired level. Also try cleaning the showerhead to remove any build ups (a maintenance issue).

It sounds like the cartridge has to be changed. Pressure balance is not working in the cartridge.

You can fix it if you can find the parts ( not easy if you can find the parts).
http://www.tlc-direct.co.uk/Technical/DataSheets/Triton/T90Si.pdf

The Triton t90si is fed from the tank in your attic.This also feeds the cold water in your bathroom.If you still have cold water in the bathroom tap,it means that there is water in the attic tank so the problem is somewhere else.I believe there is a bleed valve on these showers so maybe that is the problem. It may also be that the pipes are clogged up with dirt or limescale.The water filter may need cleaning. Hope this will help with your thinking on the problem.

I have a Triton Ivory 111 shower, twice this week the water as just stopped flowing mid flow, presure ok and power still on what could be the trouble??
Stew.

I would check utube first for possible repair. not knowing whether yours is gas or electric, I would have to recommend contacting the manufacturer.

pump needs attention and the heating element has burnt out
pump needs water to run and the heater element needs water to keep it cool

You could have mineral deposits on the temperature probe inside of the unit. If you remove the heater and purchase a bottle of lime and scale remover (lime away) to put inside of it. Let the unit sit full of water and chemicals for 24 hours. Flush out the unit to remove any residue. You may see the water is brown if you have a lot of buildup. Reconnect unit and test your settings. If this doesn't work, install a anti-scalding device, available at a plumbing supply store.

Most conventional showers have brass seats or rubber seats that can deteriorate over time. these will leak or dribble and not maintain your temp.. Rubber and brass seats are a fairly common and easy replacement. It sure beats trying to rip out a shower valve.