Furnace does not respond to room thermostat, stays off even when there is demand

Safety: Isolate power before working on wiring; wireless checks can be done with power on.

Steps:

• Check thermostat: Replace batteries, ensure it is set to heating mode and above room temperature.
• Check receiver: Verify that the receiver near the boiler shows a demand signal (LED or icon) when the thermostat calls for heat.
• Re-pair devices: Follow the De Dietrich manual to re‑pair the wireless thermostat and receiver.
• Wired systems: For wired thermostats, check that the cable is intact and firmly connected at both ends.

Professional help: If the boiler still does not respond, the control PCB or thermostat may need replacement.