This is the first time I’ve ever even tested for a gas leak in this area of a furnace. Got a definite positive reading here but I’m not sure if it should be classified as a leak, as it is near what I’d call the jets. The furnace was not running during this test.
Writeup for HVAC contractor. There will be some presence of gas present at the burner orifices when the gas valve shuts down and will take time to dissipate. Honeywell had an article about this an the correct method of testing is a device called a bubbleometer.
Lots of questions are needed. Had the furnace been recently run? How large of a leak did it detect, the detector can pick up small amounts of residue. Have you ever tried sticking the probe in the fire (haha)? Did you know that your detector can identify a cracked heat exchanger?