On most electrical installations, there is an element called a "load shedding device" between your radiators and the thermostat.
In the event of an overconsumption of electricity, the load shedding device temporarily cuts off the power supply to your radiators to avoid tripping your installation.
It is generally fixed in the electrical panel. Some load shedding devices are not compatible with the COMAP Smart Home thermostat, they must either be removed or replaced.
It is a simple manipulation, but it requires to be guided. Please call your electrician / heating engineer before carrying out this operation.