Bosch Delayed Ignition / Burner Light-Off Noise

Furnace makes loud banging or booming noise at startup

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

Dirty burner assembly, Incorrect ignition electrode position, Low primary air or blocked air intake, Gas pressure issues

Safety: Turn off power and gas. Do not continue to operate a furnace with loud ignition bangs.

Inspect burner: Remove the burner and clean ports with a soft brush and vacuum. Do not enlarge or damage the ports.
Check electrode: Verify the ignition electrode gap and position per Bosch specifications so that the spark occurs in the gas stream.
Air intake: Ensure the combustion air intake is not blocked or restricted.

If noise persists, a technician must check gas pressure and combustion settings.

Hard 4/5

Burner Assembly

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