EPH I think are the only OpenTherm thermostats which can be configured as master/slave to work up to 10 zones.
The other method is to stop using the large open/closed motorised valves just power both open with the boiler turning on, and use electronic heads on the TRV's on each radiator so each room becomes it's own zone.
The boiler is analogue, it can turn up or down as required, it can in general use two methods to turn it up and down, one is some ebus wall thermostat/hub, the other is the return water temperature. The problem with return water is it needs to flow to work, so once boiler is off, it can't use that method.
The traditional work around was to put a wall thermostat in a room normally kept cool, (so in summer it is never triggered), on the lower floor, (as heat raises), where there is no alternative heating, (not a kitchen, or even a room where the sun can heat it through windows), and with no outside doors, (clearly as when opened it will cool the room).
The problem is there is rarely such a room, so methods used are, multi wall thermostats, or two thermostats in the same room, one on the wall, and one on the radiator, the latter can work, it did in my mothers house, but not easy to set up so the two thermostats don't fight each other but complement each other. What we had was thermostats in hall, the TRV set around 17 - 19ºC and the wall set to 19ºC so as the room peaks the wall thermostat will in fullness of time switch off boiler, but only on warm days, and the TRV will allow fast recovery of hall temperature.
But the easier method to set up is where the TRV's are linked to a wall thermostat/hub, Honeywell EvoHome was one of the first
allowing you to set many rooms from a central point, but I am jumping ahead.
Many thermostats/hubs can connect to the boiler in two ways, one digital (simple on/off) the other analogue (slowly change output [flame height] up and down) the latter is best, but the connection to the ebus is sometimes limited to thermostat of same manufacture as boiler, OpenTherm is designed to work on many makes, but not all.
So there is no one system which is best, Wiser seems very good, but also these systems can be expensive. An electronic TRV head can vary between £15 and £80 each, I used 5 x eQ-3 heads at £15 each in 2019 but they seem to have gone up in price, and do not connect to the wall thermostat/hub, the Terrier i30 is the same, I moved to the TP-Link (Kasa) to replace my Energenie Mihome head which has been smashed, those two do connect to the wifi rather than the bluetooth with eQ-3 but as yet not got them to connect to my Nest Gen 3 wall thermostat, which seems to be some what of a white elephant, and does not interconnect with anything which helps control the home even if it is OpenTherm.
Once you have looked at the prices come back, as most are put off when they see how much it will cost. I like the Hive idea, where although no OpenTherm, it allows one to slowly add to the system, but main thermostat must be in a cool room as it stops accepting a demand for heat at 22ºC.
Many seem to be made for two main zones, the Wiser has a three zone model you will not need the third zone with a combi boiler, but the two zone is CH and DHW so needs the three zone one to do two CH zones.
Many seem to use two thermostats and link, but only EPH seems to do it properly, and they don't connect to TRV heads, basic why would you want to zone the zones?
