In a normal system it stops the boiler cycling and turns it off when the room stat temp is reached. You must know that?
I of course must agree with the anti-cycle function, but the problem is to work, the two thermostats need to be very carefully matched, if the TRV turns off too soon the wall thermostat will not work, and too late the latent heat collection is messed up. I know in my own hall the temperature 1.5 meter from front door and 300 mm high (TRV) is between 2 to 4 degrees lower to the temperature 5 meters from front door and 1.5 meters high, it is not being different which is the problem, but the variation between the two changing.
My computer shows TRV temperature,
so all it needs is an IFTTT command, it this (current equals or exceeds target) then that (switch off boiler) would be better maybe other way around, if any target exceeds any current then run boiler.
There should be no need for a thermostat on the wall, just a hub to collect information and act upon it.
5ºC is the frost protection setting
The question was when did they change the limit for the "Heat on Demand" function. This links with what I was saying to
@denso13 the thermostat function of the Hive wall thermostat is really to stop the room over heating if the TRV fails, under normal circumstances the wall thermostat does not set room temperature, it is set lower than required so if the batteries fail in the TRV it will still keep other rooms supplied with hot water, but it is the "Heat on Demand" function which does the real work, so if any TRV demands heat the boiler will run, even if wall thermostat is over the set temperature, so the TRV heads actually set room temperature, the wall thermostat function is only a fail safe.
There was talk about allowing the user to set the upper limit, but as far as I knew, it was set to 22ºC after which the heat on demand function stopped working. You could set the thermostat higher, but this would result in the heat on demand function being in essence disabled.
As long as the wall thermostat is put in a room not normally going to exceed the 22ºC this is not a problem, i.e. the hall, but it is possible a living room could exceed the 22ºC.
Setting a TRV is maybe easy with a differential thermometer, we are told around 15ºC difference between feed on return, but with just the computer recorded temperature it takes some time using trial and error to get the room up to temperature quickly but not over shoot, all down to the lock shield valve setting. If the flow is too high the radiator gets too hot before the TRV can close, and it over shoots, and if to low room does not reach temperature, but once set the radiator never really reaches full temperature and neither does it fully cool down when using a modulating boiler, the boiler and TRV's work together removing nearly all the hysteresis associated with an on/off thermostat, as they gradually open or close.
Does not work quite so well with an on/off boiler, but still works.
What seems uncertain is what if any gain is there with a correctly set up set of TRV heads, and an OpenTherm link to boiler?