Boiler does not respond to room thermostat; heating does not start even though boiler is powered.

Safety: Isolate power before working on control wiring.

Steps:

• Check thermostat: Ensure the room thermostat is calling for heat (set temperature above room temperature) and that its batteries (if wireless) are good.
• Bypass test: At the boiler’s room thermostat terminals, temporarily link the two control terminals (refer to Attack wiring diagram). Restore power and see if the boiler starts heating. Remove the link after testing.
• Inspect wiring: Look for loose or damaged wires between the thermostat and boiler.

Technician: If the boiler does not respond even with a link, the PCB input may be faulty and needs professional diagnosis.