My Worcester Greenstar CDi Boiler doesn't switch off?

I have a Worcester Greenstar CDi Condensing Boiler linked to a Drayton Lifestyle Controller. Just recently, we noted that the house was very warm and discovered that the boiler is now continuously 'on'. Ie, despite the controller (timer) being 'off', the boiler is on. When the timer is timed off, the thermostat is also off - which we believe is correct - however, the boiler remains 'on'. ANy ideas of how to fix or what is wrong? NB: I have replaced the controller (timer).