my bg 330 condensing boiler wont turn off?

any idea why my 330 bg boiler has suddenly decided it doesnt want to turn off. even when my timer is removed and the hall stats are down to 15. i have to turn the boiler off at the boiler panel on off switch or turn the control down to 0. i have checked the pcb and it looks good, no burning on the board.

mick
June 2015