Boiler does not respond to the room thermostat; heating remains off.

Safety: Turn off the power supply before working on control wiring.

Steps:

• Replace batteries in the room thermostat if wireless.
• Check that the thermostat is set to heating mode and above room temperature.
• Verify that the receiver indicator lights show a call for heat when the thermostat is turned up.
• Inspect the control wiring at the boiler terminals according to the IVT wiring diagram.
• If wiring and settings are correct, replace the thermostat/receiver or investigate the boiler PCB input.