What the air pressure switch does

It confirms that the required pressure differential or air flow exists before ignition is allowed.

Why it is important

If the fan does not properly remove flue gases or if the air path is blocked, the control unit should not release fuel.

What might cause a failure

  • Fan not reaching the required RPM.
  • Clogged air duct or flue pipe.
  • Clogged or torn pressure switch tubing.
  • Condensate inside the sensing line.
  • Faulty pressure switch.

Example

If the fan starts but no spark ever follows, checking the air-proving circuit is a key step.

Safety

Do not bypass the pressure switch to make the burner operate. It is a critical safety device.