Hi i've got a worcester bosch highflow 400 rsf,just had worcester bosch out to it 2 months ago,they fitted a new dhw heat exchanger,pump and serviced it. Its been great until i switched ch on it was on for about 1 hour then i turned it off using room stat,but now it not supplying hot water and even when CH switch is off and DHW is on it is heating up the radiators with no green demand light on,ive checked to see if the diverter valve is energising and it is any ideas many thanks Dave.