worcester bosch 28i junior

Hi guys, First post so be kind! My boiler is a Worcester Greenstar 28i Junior. The problem is as the title says, Central Heating is fully working but come to turn the taps on and no hot water. With the CH off, the DHW starts of warmish and the goes ice cold. with CH on, DHW comes out hotter...

Can anybody please help? I am having trouble wiring in a single channel hive system to a Worcester Bosch Greenstar 28i combi boiler. I am trying to use the old wiring, but have had to change the backplate as it wasn't compatible. I have 240v supply going in to Hive on L and N, with 240 going out...