Burner fan starts but no ignition occurs — where the sequence stops

Why the failure stage is important

If the fan starts, it means the operating command has already reached the burner. The next step is to check if pre-ventilation is completed and if an ignition command is issued.

What to check

• Whether pre-ventilation is completed.
• Whether the transformer or ignition system is activated.
• Whether there is a proper spark.
• Whether the designated fuel valve opens.
• Whether an air pressure switch or another interlock fails to confirm the condition.

Example

If the fan is running but ignition is never heard or appears, do not start with the flame sensor. First, determine why the sequence does not reach the ignition stage.

Basic rule

Burner diagnosis is performed by following the control unit's sequence step-by-step.