Electric shower cycles hot and then cold. Any ideas how to fix this?

My Triton t100xr electric shower keeps alternating hot and then cold water. Every time the shower goes cold the 'low pressure' light turns on.

Water pressure seems normal. Also tried cleaning the shower head and flexible pipe, and changing the thermal cut-off device, but this made no difference.

Does anyone have any ideas?
John, November 2015


done
There is obviously not enough water flowing through the shower,is the temperature dial set correctly i.e. turned to a colder setting,has there been anything done to the water supply lately.there is a filter on the inlet in the valve that could be blocked

toptrish, November 2015
link Click here to see other fixes for Triton.