Furnace is running but radiators are only lukewarm and house does not reach set temperature

Safety: Adjust only user‑accessible settings unless you are a qualified technician.

Steps:

• Check thermostat setting: Ensure the room thermostat or De Dietrich controller is set high enough and not in economy mode.
• Verify heating curve: If using outdoor compensation, increase the slope slightly in the controller menu to raise flow temperature.
• Open all valves: Confirm that radiator valves are open and not stuck.
• Check boiler flow temperature: Increase the maximum heating temperature within safe limits (e.g., from 60°C to 70°C) if allowed by the manual.

Professional help: If performance remains poor, a technician should check pump sizing, system balancing, and heat exchanger condition.