Boiler displays E08, burner stops, and the circulation pump may continue to run. Often associated with flue gas temperature issues.

Safety first: Turn off power and gas. Flue gas components can be very hot; allow cooling before touching. Flue gas problems can be dangerous—do not ignore repeated E08 errors.

Step-by-step checks:

• 1. Visual flue check: Ensure the flue terminal is unobstructed and correctly installed according to Viadrus instructions.
• 2. Inspect flue gas sensor: Locate the flue gas NTC in the flue collector or hood. Check that it is firmly fixed in place and that the cable is intact and properly connected to the PCB.
• 3. Clean heat exchanger: Soot or dust on the heat exchanger can raise flue temperatures. Remove the burner and clean the heat exchanger surfaces with a soft brush and vacuum, following Viadrus service procedures.
• 4. Sensor test: With power off, measure the resistance of the flue gas NTC and compare with specification. Replace if open, shorted, or far out of range.
• 5. Reset and monitor: After cleaning and/or replacing the sensor, reset the boiler and monitor operation. If E08 recurs, a more detailed combustion and flue analysis is required.

When to stop: Persistent flue gas overtemperature faults require a professional with flue gas analysis equipment. Do not continue to operate the boiler with recurring E08.