View the thread, titled "Hive thermostat recently installed. Ideal h15 boiler ..heating working but hot water is off" which is posted in Boiler Advice Forum on UK Plumbers Forums.
Needs tracking out but in essence the feed to cylinder thermostat needs connecting to terminal 3 on hive.
You really shouldn't need to ask these questions the Hive uses a industry standard back plate any competent electrician should be able to sort it first time.
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Reply to the thread, titled "Hive thermostat recently installed. Ideal h15 boiler ..heating working but hot water is off" which is posted in Boiler Advice Forum on Plumbers Forums.