New Thermostat

Hi, I dropped and broke my thermostat. I bought a new one and paired it straight away - the heating is working as normal but the hot water does not. Any ideas on what I need to do? The old thermostat is still showing on the app - but I cant see any way to delete and the new thermostat has been assigned as room 3, I wondered if this had anything to do with why the hot water will not work?

Many thanks