Home heating automation

And what thermostats are fitted to the new house. Are there basic wired stats in the two zones?

Wait till you get in and can figure how many independent zones you have, and and maybe post a picture of them. Good luck with the move in, you'll have your hands full with that for a while, no rush on heating control while summer is on the way.

Since they bought Nest they've never shown any interest in the product, other than the yellow pack Nest E, which was a low(ish) price bog standard single zone heating only device. It reminds me in many ways of the US attitude to European standards, products and practices. Like their oversized retro truck tractors, which can't be used on European roads, they moan that we don't buy their automotive stuff, failing to understand how superior the technology is this side of the pond.

Whatever, the 50% off from Tado X is strange, Google have no known stake in Tado, so it must be a redundancy packet of sorts for Nest owners, negotiated with the German firm. If I was a Nest owner, I'd take it up as soon as it becomes available. Perhaps the stats will continue to work from the Home app, or other smart thing apps, but it will probably be very limited. It's in keeping with the general insular rethoric coming from the US. Who'd buy a Tesla now?

Tado receiver will work as CH only for combi boiler, or as CH and HW 2 zone controller with identical CH and HW relays to the Nest receiver. Tado has the options of smart radiator TRVs for individual room control, something Nest never considered

Judging by that paucity of posts here, I would say it's not particularly popular. On the plus side, it was the only other of the new generation smart stats that had a wired version like Tado, to facilitate a straight swap for wall mounted basic wired stats. On the minus side, it never had hot water relay equipped receiver or HW timing in the app, it was very much a stat for European style installations with combi boilers and direct HW.

On the subject of OpenTherm, there are some efficiency advantages to be had, as boiler flow temperature is 'known' to the thermostat and will be adjusted to the minimum to maintain set temperature while increasing condenser boiler efficiency. Most smart stats controlling conventional boiler switching using simple on/off control will achieve a degree of similar efficiency control by using Proportional Integral Differential switching of the boiler in response to the difference in set and actual temperature. Tado does this using modulated bursts of boiler cycles. Your Nest Thermostat receiver, the 'Heatlink' box, has OT terminals for wiring to OT enabled boilers, so you could have tried it out on your Combi boiler if you wished. The Tado Wired stat also has OT wiring terminals, but would need wiring from the current Nest Thermostat location to the Heatlink location, as most Nest are wirelessly installed. An isolated cable pair is required for low voltage OT stats or their OT equipped receiver. If using the Tado wireless stat for OT control, you have to specify the one with the European reciver, which has OT wiring terminals as well as CH on/off relay, but no HW zone relay. In @gar's case. He would need the irish/UK version with a HW relay in the receiver to control both CH and HW zones. This model does not have OT terminals or control.

If you opt for an OT connection to a combi boiler, the Tado does have some app control of Direct HW temperature from the combi as it can communicate with the boiler's software, and afaik, it can also turn on or off the HW preheat, which keeps a small amount of HW preheated in the boiler's heat exchanger to reduce HW time lag to the tap which is a feature of direct HW combi boilers. I'd imagine neither of these two features are something you'd adjust frequently, set and forget.

Excellent, though you'd expect Ideal to have included the 5 pin plug, but perhaps it prevents numptys accidently wiring 220v into the low voltage data pins. TadoX receiver with HW relay from Tado UK site can also do OT according to the bumf.

https://uk.shop.tado.com/products/wireless-smart-thermostat-x-starter-kit-incl-programmer-with-hot-water-control-and-opentherm

Tado.com site for European market has the receiver with CH only and OT terminals. https://shop.tado.com/products/wireless-smart-thermostat-x-starter-kit

You'll have to swap the twin immersion toggle for a smart switch. You can choose either of the immersion elements to use with this, or both together if the switch capacity is sufficient. This one below is a single pole but is rated for 40 amps, which would allow both elements to run together for maximum full cylinder heating.

https://www.amazon.ie/Immersion-Heater-Switch-Control-Assistant/dp/B0CKTFNCB3/ref%3Dasc_df_B0CKTFNCB3