I have to admit I changed my Horstmann DRT2
for a
newer model and the easy press up/down was lost even when the two looked so similar the thermostat I have now
very easy to use, although not quite so easy to program to start with.
But what you need to understand is my old oil boiler is very different to your modern gas boiler, this
is your main control, set correct your boiler should not switch off/on when heating is required, it should turn down, only when at minimum output should it turn off, if you boil a kettle it does not take long to boil, but it takes a very long time to turn all the water into steam, and you boiler is designed to extract the energy that is used to turn water into steam called latent heat.
To do that the return water temperature is important, it needs to be cool enough to turn steam into water, so each radiator has a lock shield valve which is set so the radiator water cools around 15°C as it passes through the radiator, and also the TRV which closes as the room gets warm, the simple one shown works over around 2°C fully closed to fully open, so it does not have °C marked on it as it will vary slightly it will be around 2½ for 20°C.
As it closes more water is at first forced though radiators still open, and then the by-pass valve opens, the boiler monitors the return water temperature and as the temperature increases it slowly turns down, this maintains the home as a constant heat, with very little hysteresis. So not only using less energy, but also better control.
However it has a problem, as summer returns it can't fully switch off, so if left all summer the heating would be cycling on/off to test if required, so we put a thermostat in an area normally kept cool as we want to set it at 17 to 18°C so on a day where it is likely to warm up, heating does not come on, in theory a room on bottom floor as heat raises, with no outside door, and no alternative heating, and that room has no TRV fitted, well in practice often no such room.
So we go for a compromise, the hall has an outside door, so we fit a TRV and a wall thermostat, so when outside door is opened the TRV turns full on to re-heat the hall, but at 16°C it starts to close, so at 18°C nearly fully closed, and the wall thermostat set at 18°C will only work on warm days.
We could of cause use a human machine interface (HMI) in the form of a simple switch, and do away with the thermostat, and manually turn off heating when not required.
Up to this point looking at likes of a care home where heated all day and all night, but often we want to turn off heating when we go to bed, or go to work. If turned fully off then it can take a long time to re-heat home, so we instead turn it down, this also gives frost protection, so turn that hall thermostat to 16°C and it will switch on/off for a short burst to keep hall warm, but since the TRV is wide open, rest of house will get very cool, so by also using a programmable TRV we can turn heat down in hall and still keep rest of home reasonable warm so does not take too long to reheat.
This house takes ages to reheat, I have an open grate and loads of wood, but lazy, and have never lit a fire since I have lived here, so for me the geofencing turning on heat before I get home is good, but last house living room had a 4.5 kW gas fire, and a 3.5 kW fan assisted radiator and a 4 kW standard radiator in the living room, so 15 minutes and room warm again. So last house no need for geofencing.
Every home is different, mothers house huge problem with bay windows over heating the living room, wind direction also changed how her house heated, so there is no one compromise fits all. Yes with some integrated system which would cost an arm and a leg we could have twin matrix fan assisted radiators which can heat or cool each room as required. But few can afford that, so we work on near enough engineering, but to select what is likely to work, you need to understand how it works.