Safety: Turn off power before changing thermostat wiring.

Verify wiring: Compare thermostat wiring to the NTI installation manual. Ensure call for heat terminals are correctly used.
Bypass test: Temporarily jumper the call for heat terminals at the boiler. If it starts, the issue is in the thermostat or wiring.
Check settings: Confirm the control is configured for external thermostat operation and not locked in manual or test mode.
Replace thermostat: If wiring is intact and the boiler responds to a jumper, replace the thermostat.

Boiler display shows normal operation but thermostats do not call for heat or boiler does not respond to call

Possible Causes