This does not happen with every use, but sometimes twice in 5 min shower.
I've checked TCO while cycling (stays on) and temp sensor? in outlet line (stays low res.).
I know the temperature is set by the rotary control which is basically a mechanical gate valve, so if flow rate and pressure do not vary, then how could this device cause the temp to cycle.
What does the cartridge assembly do?
Any advice much appreciated, thanks

Tony, April 2007

Fixed it myself.

It's probably the same fault as Goosepimpled had in March, but didn't create as much damage to the wiring as he/she had, and he/she is still waiting for an answer!

Check the temperature sensor on the outlet pipe, it's wired in series with one of the heater elements, so if it's become unstable , the power to that heater goes on and off.

The clue is in the melted plastic covers on the spade terminals.
It means that the device itself is generating so much heat due to the internal switch contacts arcing.
You have to buy the complete outlet pipe assembly (the sensor is not available seperately), but it does come with new wires and terminal block!!!

Incredible as it sounds , the part is actually much cheaper direct online from Triton spares dept than from other suppliers on the net. (83303160 £20.76)

I hope that helps someone else out there.

Tony Robson, May 2007