Boiler shows flue/venting error, burner stops shortly after ignition attempt

Safety first: Turn off power and do not operate the boiler if you suspect a flue gas issue. Risk of carbon monoxide exposure.

• Inspect external flue terminal: From outside, visually check that the Nibe concentric flue terminal is free from obstructions (ice, leaves, nests). Do not modify or dismantle the flue yourself.
• Check condensate drain: Ensure the condensate pipe from the boiler to the drain is not frozen or blocked. Thaw gently with warm (not boiling) water if frozen and clear any visible blockage at the trap outlet.
• Listen for fan operation: On start-up, you should hear the fan run before ignition. If the fan is silent, the fan motor or control board may be faulty.
• Do not bypass safety devices: Never bridge or bypass flue gas sensors or pressure switches. This is dangerous and illegal in many regions.
• Contact a Nibe service technician: A professional must test the flue gas sensor, fan speed, and flue integrity, and replace the faulty Nibe flue gas sensor or fan assembly if required.