F.36
Vaillant Flue Gas Recirculation / Flue Blockage Detected

F.36 error, boiler shuts down shortly after ignition, may be accompanied by flue gas smell outside

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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

Incorrect flue terminal positioning, Obstructed flue or air intake, Damaged flue seals, Strong wind causing recirculation at terminal

How to Fix / Troubleshooting

Safety: Turn off the boiler and do not use it until the flue system is checked. Risk of carbon monoxide exposure.

User checks:

  • Visually inspect the outside flue terminal for obstructions or damage.
  • Ensure no structures or objects have been added near the terminal that could cause recirculation.

Professional checks:

  • Inspect the entire flue system for correct installation, slope, and integrity.
  • Check flue seals and joints for leakage.
  • Verify combustion values with a flue gas analyser.

Only a qualified engineer should work on the flue and combustion system.

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Repair Difficulty

Professional Required 5/5

Required Part

Flue System Components
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