If you notice that your home struggles to reach the set temperature of 21 and often stays around 19.5-20, before thinking there might be a malfunction, it could be due to incorrect boiler temperature settings.
The Siemens RDE10 Thermostat, designed to meet all your heating needs and save on gas boiler consumption. If programmed correctly, it can keep your home warm at the hours you decide, while during the day when the house is unoccupied, you can select an economical temperature.
The Perry 1CR CR309/S thermostat is an older model still widely sold for its ease of programming and use. Its price is also very advantageous, providing a complete regulator to use with your heating system according to days and times and two temperature levels (Comfort and Economy).