i have a TRITON T100E electric shower running from a FERROLI F30 combi boiler. the problem is when i pull the cord even before i turn the shower unit on the system over heats with a trickle of boiling water for a few seconds. when i switch the unit on it runs cold but i have to start with the heating switch at it s highest setting then i have to turn it down gradually sometimes on doing this the system over heats and there is not much water coming out of the shower.
As Dasherman says, your Triton should have an independent cold feed off the mains and be unaffected by the boiler function, in the same way as the cold tap at the kitchen sink is independent. There's a possibility the shower installer supplied the shower heater from the boiler hot water outlet, but if the trouble just cropped up, I'd say the shower thermostat has gone kaput.