Remeha RF boiler constantly on heating up the radiators?

I've had a new Remeha RF boiler installed in April 2008 and everything has been fine for a few months.

In the last two weeks the boiler is remaining on constantly despite how I set the controls.

The control panel has timed where you set the time for the boiler to come on and go off, minimum temperature (where the boiler is but the minimum temperature set on the dial is maintained) and maximum (where the heating is on to maintain the maximum temperature set on the dial).

Whatever I do the heating remains on so I have resorted to turning the boiler off at the main fuse box. Please help?