Had the same problem - you need to replace the hot water flow temperate sensor (two minute job). Part available from plumb centre - part number 800320 (E23-839).
How to fit:
Remove outer casing and retaining bars from control panel to gain access. The sensor is located on the output of the hot water pipe (left hand side - facing the boiler).
Isolate power to bolier.
Turn water off - open tap to reduce pressure.
Remove connector to sensor.
Replace sensor - reconnect and refit casing
Turn water and power on and test.
Adrian, July 2005
