UK user - central heating and hot water control - initial questions

Hardware
21

Hopping on to this thread today. Can somebody help me here with terminology and general systems advice. We live in the UK - have an oil burner (furnace) that runs central heating and hot water via indirect coils - open vented system - I think it is called.

Currently have an old Honewell controller that allows for programming of up to 3 sessions of heating and/or hot water per 24hr cycle and options for different timings at week ends.

To bring this into Home Assistant (and avoiding any Cloud based services) I think we need something like this.

240v mains “Hub” that has power to it and solonoids within it to switch on the boiler (furnace) and switch on and off the two circulation pumps that exist to pump water round the hot water system and the central heating system. This needs to have Zigbee in it to communicate with HA

Then initially perhaps a Zigbee thermostat that can sit in the middle of the house and allow for general control of heating and hot water system manually.

All existing radiators have mechanical thermostatic control valves on them at present. We generally leave these set at a low setting for frost prevention. Only having warmer settings in the rooms we actually use.

Later on we can perhaps fit one or two Zigbee thermostatic control valves so that we can alter the timings of heating for say the bathroom.

Questioins

  1. What is the generic name for this 240v hub that handles the switching on and off of mains power to the boiler and circulating pumps and has Zigbee within it?

  2. I was leaning towards Nest as this is what my heating engineer is used to. However various videos seem to prefer EcoBee thermostats. These seem to the the user operated interface to the “hub” Nest or EcoBeeAre these preferable?

  3. I wish this to be able to operate their usual timing program if HA goes down. Might there be a couple of buttons to override the central heating or hot water system so if the Zigbee network is down then one press either starts/stops that function?

As time goes on I would like to add further features ising HA as a base. Thanks.