The Triton has two electric heating elements that give two fixed heat outputs. The temperature of the water emitted is controlled by how much water is fed through the heater(s) If the shower is getting too hot it is likely that there is insufficient water flowing through the heating elements. Then because it is getting too hot, the "Temperature Limiter" is operating which turns off the heating element(s) so that you don't get scalded. Then, when the elements cool and it resets, the elements come back on and the process is repeated.
It is possible, now that summer has arrived
the incoming mains water is a few degrees warmer than it is in the winter so does not need as much heat adding by the electric elements. Lowering the number you normally use on the control knob (which increases water flow) maybe all that you need to do.
If you cannot stop it getting too hot by increasing the flow of water enough by turning the shower control knob to a lower number, then you need to look at other sources of water restriction. For example.
Does your mains water supply have a sufficient flow / pressure for the shower? (minimum, 9 litres/minute at 1 bar)
Is something else being used at the same time that causes the water pressure / flow to drop (eg WC, washing machine, another tap etc.,)
Is the shower inlet filter blocked?
Has a stop tap / isolator somewhere in the shower supply line been turned down?
Is the shower head blocked with limescale preventing sufficient flow through the shower?
