Daikin Altherma HT User Manual page 5

Hot water preparation in detail
Your system is set up to heat the water in the cylinder at the time
when it is cheapest. If you have Economy 7 this will be during
off-peak periods. If not, it will be during the day when the air
temperature is higher.
Programmable room thermostat
You may have a room thermostat installed in
your property. It would be located in the hall or
within certain rooms. It controls when the house
is heated, and to what temperature.
It is likely the thermostat has been set to
heat the house to 21°C in the early morning,
lunchtime and evening, with a cooler 18°C
at other times from Monday to Friday.
At weekends, it is set to 21°C from early morning
until late evening, with 18°C over night.
Heat emitters: radiators
Most radiators are fitted with Thermostatic
Radiator Valves (TRV's) as shown in the picture
which ensures rooms will not become
too warm.
Temperatures are represented by numbers
or roman numerals I, II, III, IIII. The higher the
number, the warmer the room temperature.
Each valve should be set according to the
temperature you wish to achieve.
Underfloor heating (UFH) and/or
fan coil units (FCU)
If UFH heating is installed you may see
a manifold in your airing cupboard
or similar with pipes going
into the floor. This will heat
your floors, which in turn
heat your home. If FCU are
installed you will see them
on your walls. FCU operate
in a similar way to radiators,
but a fan in the unit
pushes heat into the
space around it.