Vaillant Ignition Sequence Interruption

Boiler fan runs but burner does not light, no error code displayed

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.

Possible Causes

Faulty air pressure switch (on older non-condensing models), Blocked flue or air intake, Weak spark from ignition electrode, Gas valve not opening despite call

How to Fix / Troubleshooting

Safety: Turn off gas and power if repeated failed ignition occurs.

User checks:

Inspect the flue terminal for obstructions.

Professional checks:

Test the air pressure switch tubing and switch operation (where fitted).
Inspect and clean the ignition electrode and check spark strength.
Verify gas valve operation and correct voltage during ignition.

Repair Difficulty

Hard 4/5

Required Part

Ignition Electrode

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