A22
Hoval Flue gas spillage / CO hazard

Furnace indicates flue gas recirculation / CO alarm from external sensor

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Blocked or undersized flue on Hoval furnace, Negative pressure in boiler room, Damaged flue seals, Faulty or mispositioned CO sensor

How to Fix / Troubleshooting

Critical safety: If a CO alarm is active, evacuate the area immediately, ventilate by opening windows and doors, and shut off the furnace and gas supply. Do not re-enter until the area is safe.

  • Do not operate furnace: Leave the furnace off until a qualified technician has inspected the flue system and combustion.
  • Check ventilation: Ensure boiler room vents are open and not blocked.
  • Inspect flue visually: From a safe location, look for obvious damage or disconnection of the flue pipes.
  • Test CO sensor: Once the system is safe, have the CO sensor tested or replaced if faulty.
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Repair Difficulty

Professional Required 5/5

Required Part

Flue System
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