Boiler

Need some advice. I have an ideal boiler he15 and the heating and hot water is off but the boiler it displays C and it keeps firing up like it’s on continually. What does that mean. Whatever I switched on last ie if I put the heating on for an hour, the heating is still on after an hour and boiler keeps firing up even though it’s off. Not sure if it’s to do with anything, but recently changed the pcb ?????. Thanks