Boiler and home thermostat connections 

Connection schemes and connections in detail,
between boiler and thermostat.
The boiler of private houses is a simple plant:
a circuit breaker in the distribution switchboard protects the line
which supplies the thermostat and the boiler, the contacts between the boiler and the thermostat are called clean, ie they are free of tension, between them
only closing and opening takes place.
If a solenoid or motorized zone valve is present in the heating system, then the contacts are live.