Boiler display works but no response to heating demand from room thermostat

Safety first: Isolate power before accessing control wiring.

Steps to check:

• Check that the room thermostat or programmer is powered and set to call for heat.
• If wireless, ensure the receiver shows a signal and is correctly paired with the thermostat.
• Inspect the low-voltage control wiring at the boiler for loose or broken connections.
• For simple on/off controls, a temporary link across the boiler's room stat terminals (by a competent person) can confirm if the boiler responds.
• If the boiler fires with a link but not with the thermostat, the thermostat or its wiring is faulty and should be replaced.

Warning: Do not leave a permanent link in place; this would bypass temperature control.