In the UK, central heating is common, where either a gas-fired (in most cases), wood or oil-fired (in remote parts where there is no piped/mains LNG exists) heats radiators around the home to about 60 degrees Celsius, or underfloor heating where there is a mixing manifold which delivers heat at an average 21 degrees Celsius.
The boiler is generally in two formats, a system boiler or combi boiler.
The system boiler heats a tank of hot water (thermal heat store) and hot water for outlets or radiators generally circulates through the tank. Hence there can be hot water without the need for the boiler to come on. In this case, the tank would have a connected thermostat which switches the boiler on when the tank temperature drops. In this scenario, the tank has an electric immersion heater (usually 3-6Kw) which acts as a backup if the boiler fails.
The other format, combi (combination) is where the boiler provides instant hot water to outlets or circulates through radiators.
In the case of the system setup, a TRV on a radiator should switch on the boiler if tank temperature is low (unless the radiator flow/return circuit goes direct to the boiler) and there is demand (radiator is below desired temp). When radiator is hot (above desired temperature) and tank is hot, boiler should be turned off. In the combi setup, the TRV should control the boiler switch directly. In both system and combi setups a single thermostat would control when the heating comes on; this isn’t great because houses should be zoned with more thermostats but that’s where smart TRV’s and smart temperature sensors can help drive efficiency and automation.
It’s worth adding that the heating controller is used as a time switch for separate programmes for hot water (system boiler setup only) and central heating. To control whether heating is on / off or hot water is on / off, a Sonoff Dual Lite can be used with a programmer like the Honeywell model shown so switching is 2-way.
More modern houses or passive houses would rely on electricity to heat electric underfloor heating with each room being a zone and an immersion heater would heat a thermal store for water outlets but these are less than 1% of the housing stock.
Where there are apartment blocks, larger ones would be solely electric heated as they don’t have boilers and smaller blocks are normally with gas boilers.
Of course there are a wide variety of homes but the majority rely on main gas boilers.
In my instances, all radiators except one (emergency heat dump for boiler if all TRV’s are closed) would have smart TRV’s and either the TRV thermostat or a separate smart thermostat will control when the boiler needs to fire.
I need the TRV (or separate smart thermostat) to trigger the boiler, but there needs to be intelligence. For example, if I have two TRV’s both needing heat, an on trigger is sent to the boiler but the off trigger can only be sent when all TRV’s are sending off. It’s not complicated logic. Until this is here, I can’t use my TRV’s as they would just be left in the manual on mode wasting battery power!
Ideally, the groupings could help control this functionality but if there was a separate heating function, designed specifically for this purpose, the setup could be easier for less savvy users.
Less essential, is the adding of TRV’s to cast with simple override functions or controlling groups of TRV’s with the same schedule. By example, my Tado setup in a property that I have multiple rooms on Airbnb has a schedule with a different target temperature set every hour of the day. This way, if a guest cranks up the temperature, at most, it will heat the individual room for an hour until the new target temperature takes effect. The same schedule is applied to all bedrooms (one group), another group is for the living room, hallways and kitchen; and a third group for the bathrooms. This way, I only have to configure three groups and the fifteen radiators rely on those group settings.
Here an example of a radiator with a Sonoff TRV compare to a traditional TRV, a very old (but still working) thermostat and the heating controls for a system boiler. The thermostat and heating controls all switch at 240V.