Boiler does not respond to room thermostat, stays off even when there is a demand for heat.

Safety: Isolate power before working on control wiring.

• Check thermostat settings: Ensure the thermostat is set above room temperature and not in OFF or holiday mode.
• Battery check: Replace batteries in wireless thermostats or wired digital stats if applicable.
• Bypass test (engineer level): At the boiler, temporarily link the thermostat terminals. If the boiler starts, the thermostat or its wiring is faulty.
• Replace thermostat: Fit a compatible Thermona-approved thermostat or controller if the existing one is defective.