greenstar 24i. No hot water?

No hot water delivery, the boiler kettles on the main heat exchanger with HW demand. Central heating demand no problems. A brief history, the previous owners had the rad circuits replaced as the pipework was blocked. Upon purchase of property I moved the boiler to the loft without using the appliance. My guess is the small heat exchanger . Upon kettling the boiler stops as normal there is no flashing blue lights and do'es not require resetting