If your NS1001 thermostat appears to be calling for heat but the boiler is not responding, check the following:
Check if the Relay Clicks ON and OFF
When the thermostat starts calling for heat, the relay should make an audible clicking sound as it switches. When it is switch off it should click again. The easiest way to do this is by putting the Thermostat into On, then increasing and lowering the temperature.
If you do not hear a click:
Check that the thermostat is correctly seated on its wall mount.
Ensure it is fitted flush against the wall plate.
Try removing and reseating the thermostat onto the wall mount.
If the unit does not click, it maybe time to upgrade your unit.
Check the Programmer (if fitted)
If your heating system has a separate programmer, it must be set to ON, 24hr, or Continuous.
If the programmer is set to Off or Timed, it may prevent the NS1001 from controlling the boiler.
Check for Boiler, Valve, or Wiring Issues
If the relay is clicking but the boiler does not start, the issue may be with the zone valve, boiler, or system wiring.
In this situation, you should contact a qualified heating engineer to investigate further.