I have to agree with "someone-else" so easy to waste money with wifi enabled. However it does seem to go in stages, so from out set you need to work out what stage you want, as next stage often means replacing it all over again.
So I will try to explain, I don't think your boiler has the option for a thermostat which connects to the boiler bus, not even sure if that boiler is a modulating boiler to start with, I think it is simply on or off? Also not sure if mains voltage control or 24 volt, this will make a difference, if 24 volt then you need volt free contacts for the controller, which knocks out Hive, but think Nest is volt free.
However the modern system uses the thermostatic radiator valve (TRV) to control, and when using these you have a by-pass valve so when they all closed there is still some where for water to go, before the TRV often there was no by-pass valve.
To use the same boiler for domestic hot water and central heating we had plans, refereed to as Y plan, C plan, W plan to name some, and some of the old installations had no way to turn off domestic hot water and leave central heating running, and even when there was, it was some times hit and miss where it simply turned off pump to get domestic hot water only.
The programmer you show often had a mechanical lock, to change from 10 to 16 programs, this was all down to if you could turn off the domestic hot water.
It was common to use the timer you show to limit domestic hot water temperature by turning on just twice a day, and central heating was often just a back ground heat, and the occupants would use other fires to heat rooms in use.
Before altering control, you need to work out what you already have? In my old house I fitted TRV upstairs only to stop bedrooms getting too hot, I fitted a second boiler for domestic hot water so I did not require a hot water tank, and converted that space into a bedroom. I would not do that today as now we have combo boilers.
However step one is likely to set heating on 24/7 on the programmer and swap the thermostat for a programmable thermostat which would likely cost around £35 and means instead of off/on at set times, it sets different temperatures at set times, typically today 6 different temperatures through the day. But that will not work if you can't control domestic hot water, it may require a motorised valve fitting and a tank thermostat to turn off domestic hot water.
Hysteresis i.e. the difference between when heating switches on to when it switches off and the amount the room temperature varies is the main reason for an expensive thermostat. So I will talk about three thermostats, the Honeywell Y6630D wireless has built in anti hysteresis software, what it does is start switching off/on before the target temperature so the heating does not over shoot, it also fails safe, i.e. if battery becomes flat, it switches off, it will not stick in on mode. The Flomasta 22199SX hard wired has six times so you can program it, but no anti-hysteresis software, the difference on/off is 0.5 deg C so better than mechanical but not as good at maintaining temperature to the Honeywell Y6630D but allows you to program (This is used in my old house very satisfied with it) the Horstmann HRFS1 seems really good, programmable loads of options, wireless, however it does not fail safe, I returned to mother's house to find it at 28 degs C when it failed to turn heating off, so in spite of good specification, I would not recommend.
So hard wired not reason not to use cheap Flomasta 22199SX but if you go wireless then you need the more expensive.
Into the wifi enabled, EvoHome would normally be what I would go for, it uses the wifi TRV heads to control 6 rooms independently, however in your case I hesitate, as not sure if you can easy fit TRV's without also fitting by-pass valve, and not sure how well it would work with non modulating boiler, as to Hive it does not have volt free contacts for the duel control model which you would need, so not sure if it could be fitted, Nest is very good, and it has volt free contacts and it can talk to MiHome electronic TRV heads so can expand, but getting the 5 volt supply to thermostat is not easy. So I would spend £35 on the Flomasta 22199SX and see if that is enough, it's easy to fit, you just turn programmer on 24/7 and let the thermostat do the times.
When you replace boiler, then decide which control system. With a new boiler it will be modulating, i.e. not fixed output, and if OpenTherm enabled you could use something like EvoHome, there are others, to adjust the boilers output, since they don't turn off/on there is no hysteresis so one can see the point in expensive controls which retain this ability to vary output, I think most wifi thermostats are able to be used to modulate rather than turn boiler off/on, the exception is Hive, why anyone fits Hive I don't know. However if your not changing boiler, and if the control is 230 volt then Hive is for you likely the cheapest option with wifi and would actually likely suit your needs, but if you do change boiler, then likely Hive goes in bin, so is it worth spending that much on an old system?
Be aware if you do change boiler, some makes only allow you to use their own modulating thermostat, others use OpenTherm so you have a whole range to select from, personally any boiler without OpenTherm I would reject. I have Bosch and they use their own Wave thermostat and it only works in one room, what's the point of that?
As a foot note, normal way to control boiler is from the motorised valve, not direct from thermostat so thermostats open valve, then once valve open it starts boiler, since motorised valves are either open or closed, any house where the home is split into zones, can only use on/off thermostats, so can't use the modulating output of boiler to the full. This is the big problem, new houses have in the main two zones which instead of improving control does the reverse, some government official has thought Oh that's a good idea, but had no idea how modern boilers work.
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