Horseman channel plus XL - heating/ hot water issue?

My HORSMANN Channel Plus XL (heating upstairs on one channel & downstairs heating on another channel with hot water on another channel) - this programmer has three settings per day on a 7 day timer, the heating was approximately installed in 2003.
The battery CR 2430 shows 2.98v.
The main issue is I can only run one program at a time, so I have to turn off central heating (up or down stairs to turn on the hot water which is an unvented mega flow.
Any practical advice or identifying the problem would be greatly appreciated.
Regards
Tim.